Motion vector restriction for out-of-frame boundary conditions

ABSTRACT

Aspects of the disclosure provide a method and an apparatus for video decoding. The apparatus includes processing circuitry that determines motion information of a current block. The motion information indicates one or more reference blocks of the current block. If a motion information constraint indicates that the one or more reference blocks are within picture boundaries of respective one or more reference pictures, the processing circuitry reconstructs the current block based on the one or more reference blocks. If a first motion vector (MV) points from a region in the current block to a first reference region of a first reference block that is outside a picture boundary of a first reference picture, the processing circuitry determines a first clipped MV pointing from the region to an updated first reference region by clipping the first MV where the updated first reference region is within the picture boundary.

INCORPORATION BY REFERENCE

The present application claims the benefit of priority to U.S.Provisional Application No. 63/298,774, “MV RESTRICTION OF BI-PREDICTIONFOR OUT-OF-FRAME BOUNDARY CONDITIONS” filed on Jan. 12, 2022, which isincorporated by reference herein in its entirety.

TECHNICAL FIELD

The present disclosure describes embodiments generally related to videocoding.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent the work is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Uncompressed digital images and/or video can include a series ofpictures, each picture having a spatial dimension of, for example,1920×1080 luminance samples and associated chrominance samples. Theseries of pictures can have a fixed or variable picture rate (informallyalso known as frame rate), of, for example 60 pictures per second or 60Hz. Uncompressed image and/or video has specific bitrate requirements.For example, 1080p60 4:2:0 video at 8 bit per sample (1920×1080luminance sample resolution at 60 Hz frame rate) requires close to 1.5Gbit/s bandwidth. An hour of such video requires more than 600 GBytes ofstorage space.

One purpose of image and/or video coding and decoding can be thereduction of redundancy in the input image and/or video signal, throughcompression. Compression can help reduce the aforementioned bandwidthand/or storage space requirements, in some cases by two orders ofmagnitude or more. Although the descriptions herein use videoencoding/decoding as illustrative examples, the same techniques can beapplied to image encoding/decoding in similar fashion without departingfrom the spirit of the present disclosure. Both lossless compression andlossy compression, as well as a combination thereof can be employed.Lossless compression refers to techniques where an exact copy of theoriginal signal can be reconstructed from the compressed originalsignal. When using lossy compression, the reconstructed signal may notbe identical to the original signal, but the distortion between originaland reconstructed signals is small enough to make the reconstructedsignal useful for the intended application. In the case of video, lossycompression is widely employed. The amount of distortion tolerateddepends on the application; for example, users of certain consumerstreaming applications may tolerate higher distortion than users oftelevision distribution applications. The compression ratio achievablecan reflect that: higher allowable/tolerable distortion can yield highercompression ratios.

A video encoder and decoder can utilize techniques from several broadcategories, including, for example, motion compensation, transformprocessing, quantization, and entropy coding.

Video codec technologies can include techniques known as intra coding.In intra coding, sample values are represented without reference tosamples or other data from previously reconstructed reference pictures.In some video codecs, the picture is spatially subdivided into blocks ofsamples. When all blocks of samples are coded in intra mode, thatpicture can be an intra picture. Intra pictures and their derivationssuch as independent decoder refresh pictures, can be used to reset thedecoder state and can, therefore, be used as the first picture in acoded video bitstream and a video session, or as a still image. Thesamples of an intra block can be exposed to a transform, and thetransform coefficients can be quantized before entropy coding. Intraprediction can be a technique that minimizes sample values in thepre-transform domain. In some cases, the smaller the DC value after atransform is, and the smaller the AC coefficients are, the fewer thebits that are required at a given quantization step size to representthe block after entropy coding.

Traditional intra coding used in, for example, MPEG-2 generation codingtechnologies, does not use intra prediction. However, some newer videocompression technologies include techniques that attempt to performprediction based on, for example, surrounding sample data and/ormetadata obtained during the encoding and/or decoding of blocks of data.Such techniques are henceforth called “intra prediction” techniques.Note that in at least some cases, intra prediction is using referencedata only from the current picture under reconstruction and not fromreference pictures.

There can be many different forms of intra prediction. When more thanone of such techniques can be used in a given video coding technology, aspecific technique in use can be coded as a specific intra predictionmode that uses the specific technique. In certain cases, intraprediction modes can have submodes and/or parameters, where the submodesand/or parameters can be coded individually or included in a modecodeword, which defines the prediction mode being used. Which codewordto use for a given mode, submode, and/or parameter combination can havean impact in the coding efficiency gain through intra prediction, and socan the entropy coding technology used to translate the codewords into abitstream.

A certain mode of intra prediction was introduced with H.264, refined inH.265, and further refined in newer coding technologies such as jointexploration model (JEM), versatile video coding (VVC), and benchmark set(BMS). A predictor block can be formed using neighboring sample valuesof already available samples. Sample values of neighboring samples arecopied into the predictor block according to a direction. A reference tothe direction in use can be coded in the bitstream or may itself bepredicted.

Referring to FIG. 1A, depicted in the lower right is a subset of ninepredictor directions known from the 33 possible predictor directions(corresponding to the 33 angular modes of the 35 intra modes) defined inH.265. The point where the arrows converge (101) represents the samplebeing predicted. The arrows represent the direction from which thesample is being predicted. For example, arrow (102) indicates thatsample (101) is predicted from a sample or samples to the upper right,at a 45 degree angle from the horizontal. Similarly, arrow (103)indicates that sample (101) is predicted from a sample or samples to thelower left of sample (101), in a 22.5 degree angle from the horizontal.

Still referring to FIG. 1A, on the top left there is depicted a squareblock (104) of 4×4 samples (indicated by a dashed, boldface line). Thesquare block (104) includes 16 samples, each labelled with an “S”, itsposition in the Y dimension (e.g., row index) and its position in the Xdimension (e.g., column index). For example, sample S21 is the secondsample in the Y dimension (from the top) and the first (from the left)sample in the X dimension. Similarly, sample S44 is the fourth sample inblock (104) in both the Y and X dimensions. As the block is 4×4 samplesin size, S44 is at the bottom right. Further shown are reference samplesthat follow a similar numbering scheme. A reference sample is labelledwith an R, its Y position (e.g., row index) and X position (columnindex) relative to block (104). In both H.264 and H.265, predictionsamples neighbor the block under reconstruction; therefore, no negativevalues need to be used.

Intra picture prediction can work by copying reference sample valuesfrom the neighboring samples indicated by the signaled predictiondirection. For example, assume the coded video bitstream includessignaling that, for this block, indicates a prediction directionconsistent with arrow (102)—that is, samples are predicted from samplesto the upper right, at a 45 degree angle from the horizontal. In thatcase, samples S41, S32, S23, and S14 are predicted from the samereference sample R05. Sample S44 is then predicted from reference sampleR08.

In certain cases, the values of multiple reference samples may becombined, for example through interpolation, in order to calculate areference sample; especially when the directions are not evenlydivisible by 45 degrees.

The number of possible directions has increased as video codingtechnology has developed. In H.264 (year 2003), nine different directioncould be represented. That increased to 33 in H.265 (year 2013).Currently, JEM/VVC/BMS can support up to 65 directions. Experiments havebeen conducted to identify the most likely directions, and certaintechniques in the entropy coding are used to represent those likelydirections in a small number of bits, accepting a certain penalty forless likely directions. Further, the directions themselves can sometimesbe predicted from neighboring directions used in neighboring, alreadydecoded, blocks.

FIG. 1B shows a schematic (110) that depicts 65 intra predictiondirections according to JEM to illustrate the increasing number ofprediction directions over time.

The mapping of intra prediction direction bits that represent thedirection in the coded video bitstream can be different from videocoding technology to video coding technology. Such mapping can range,for example, from simple direct mappings, to codewords, to complexadaptive schemes involving most probable modes, and similar techniques.In most cases, however, there can be certain directions that arestatistically less likely to occur in video content than certain otherdirections. As the goal of video compression is the reduction ofredundancy, those less likely directions will, in a well working videocoding technology, be represented by a larger number of bits than morelikely directions.

Image and/or video coding and decoding can be performed usinginter-picture prediction with motion compensation. Motion compensationcan be a lossy compression technique and can relate to techniques wherea block of sample data from a previously reconstructed picture or partthereof (reference picture), after being spatially shifted in adirection indicated by a motion vector (MV henceforth), is used for theprediction of a newly reconstructed picture or picture part. In somecases, the reference picture can be the same as the picture currentlyunder reconstruction. MVs can have two dimensions X and Y, or threedimensions, the third being an indication of the reference picture inuse (the latter, indirectly, can be a time dimension).

In some video compression techniques, an MV applicable to a certain areaof sample data can be predicted from other MVs, for example from thoserelated to another area of sample data spatially adjacent to the areaunder reconstruction, and preceding that MV in decoding order. Doing socan substantially reduce the amount of data required for coding the MV,thereby removing redundancy and increasing compression. MV predictioncan work effectively, for example, because when coding an input videosignal derived from a camera (known as natural video) there is astatistical likelihood that areas larger than the area to which a singleMV is applicable move in a similar direction and, therefore, can in somecases be predicted using a similar motion vector derived from MVs ofneighboring area. That results in the MV found for a given area to besimilar or the same as the MV predicted from the surrounding MVs, andthat in turn can be represented, after entropy coding, in a smallernumber of bits than what would be used if coding the MV directly. Insome cases, MV prediction can be an example of lossless compression of asignal (namely: the MVs) derived from the original signal (namely: thesample stream). In other cases, MV prediction itself can be lossy, forexample because of rounding errors when calculating a predictor fromseveral surrounding MVs.

Various MV prediction mechanisms are described in H.265/HEVC (ITU-T Rec.H.265, “High Efficiency Video Coding”, December 2016). Out of the manyMV prediction mechanisms that H.265 offers, described with reference toFIG. 2 is a technique henceforth referred to as “spatial merge”.

Referring to FIG. 2 , a current block (201) comprises samples that havebeen found by the encoder during the motion search process to bepredictable from a previous block of the same size that has beenspatially shifted. Instead of coding that MV directly, the MV can bederived from metadata associated with one or more reference pictures,for example from the most recent (in decoding order) reference picture,using the MV associated with either one of five surrounding samples,denoted A0, A1, and B0, B1, B2 (202 through 206, respectively). InH.265, the MV prediction can use predictors from the same referencepicture that the neighboring block is using.

SUMMARY

Aspects of the disclosure provide methods and apparatuses for videoencoding and decoding. In some examples, an apparatus for video decodingincludes processing circuitry. The processing circuitry is configured todetermine motion information of a current block predicted with interprediction. The motion information indicates one or more referenceblocks of the current block associated with respective one or morereference pictures. If a motion information constraint indicates thatthe one or more reference blocks are within picture boundaries of therespective one or more reference pictures, the processing circuitry canreconstruct the current block based on the one or more reference blocks.A first motion vector (MV) indicated by the motion information can pointfrom a region in the current block to a first reference region that is aregion of a first reference block in the one or more reference blocks.If the first reference region is outside a picture boundary of a firstreference picture of the one or more reference pictures where thepicture boundaries include the picture boundary of the first referencepicture, the processing circuitry can determine a first clipped MVpointing from the region in the current block to an updated firstreference region by clipping the first MV such that the updated firstreference region is in an updated first reference block that is withinthe picture boundary of the first reference picture. The processingcircuitry can reconstruct the region in the current block based on theupdated first reference region.

In an embodiment, the current block is bi-predicted with an adaptivemotion vector prediction (AMVP) mode. The motion information indicatesthe first MV pointing from the current block to the first referenceblock and a second MV pointing from the current block to a secondreference block associated with a second reference picture. The one ormore reference blocks consist of the first reference block and thesecond reference block. The motion information constraint indicates thatthe first reference block is within the picture boundary of the firstreference picture and the second reference block is within a pictureboundary of the second reference picture where the picture boundariesinclude the picture boundary of the second reference picture.

In an embodiment, the motion information indicates an MV predictor (MVP)candidate in a candidate list, and the MVP candidate indicates a firstMVP and a second MVP. The first MVP points to a first intermediatereference block that corresponds to the current block and that is withinthe picture boundary of the first reference picture. The second MVPpoints to a second intermediate reference block that corresponds to thecurrent block and that is within the picture boundary of the secondreference picture. The processing circuitry can determine the first MVbased on the first MVP and a first MV difference (MVD), and determine asecond MV based on the second MVP and a second MVD. The second MV pointsto the second reference block.

In an embodiment, the current block is bi-predicted with an affine modeand includes plural subblocks. The motion information indicates MV pairseach associated with one of the plural subblocks. Each MV pairassociated with the respective subblock in the plural subblocks includesa first MV pointing from the respective subblock to a first referencesubblock in the first reference block and a second MV pointing from therespective subblock to a second reference subblock in a second referenceblock associated with a second reference picture. The one or morereference blocks consist of first reference block and the secondreference block. The motion information constraint indicates that eachof the first reference subblocks is within the picture boundary of thefirst reference picture and each of the second reference subblocks iswithin a picture boundary of the second reference picture where thepicture boundaries include the picture boundary of the second referencepicture.

In an embodiment, the current block is bi-predicted with a merge mode,and a candidate list of the current block includes one or more MVpredictor (MVP) candidates. The processing circuitry can determine anMVP candidate of the current block from the one or more MVP candidatesbased on an MVP index. The MVP candidate indicates a first MVPassociated with the first reference picture and a second MVP associatedwith a second reference picture. The processing circuitry can determinethe first MV of the current block to be the first MVP and a second MV ofthe current block to be the second MVP. The motion informationconstraint indicates that (i) the first reference block pointed to bythe first MV is within the picture boundary of the first referencepicture and (ii) a second reference block pointed to by the second MV iswithin a picture boundary of the second reference picture. The pictureboundaries include the picture boundary of the second reference picture.

In an embodiment, for each MVP candidate in the one or more MVPcandidates that indicates a respective first MVP and a respective secondMVP, the motion information constraint indicates that (i) a firstintermediate reference block pointed to by the respective first MVP iswithin a picture boundary of a respective first reference picture, and(ii) a second intermediate reference block pointed to by the respectivesecond MVP is within a picture boundary of a respective second referencepicture.

In an embodiment, the current block is bi-predicted with an affine mergemode and includes plural subblocks, and a candidate list of the currentblock includes one or more affine merge candidates. For each subblock inthe plural subblocks, the processing circuitry can determine, for eachregion in the respective subblock, an MV pair of the respective regionbased on an affine merge candidate in the one or more affine mergecandidates. The MV pair includes a respective first MV pointing from theregion to a first region in a first reference subblock in the firstreference block and a respective second MV pointing from the region to asecond region in a second reference subblock that is in a secondreference block associated with a second reference picture. The firstreference block and the second reference block correspond to the currentblock, the first reference subblock and the second reference subblockcorrespond to the respective subblock. For each subblock in the pluralsubblocks, the motion information constraint indicates that each firstregion is within the picture boundary of the first reference picture andeach second region is within a picture boundary of the second referencepicture, the picture boundaries including the picture boundary of thesecond reference picture.

In an embodiment, the current block is bi-predicted. The motioninformation indicates the first MV pointing from the current block tothe first reference block and a second MV pointing from the currentblock to a second reference block associated with a second referencepicture. The one or more reference blocks consist of the first referenceblock and the second reference block. The first reference region of thefirst reference block is outside the picture boundary of the firstreference picture. The processing circuitry can determine the firstclipped MV by clipping the first MV such that the updated firstreference block is within the picture boundary of the first referencepicture. If the second reference block is outside a picture boundary ofthe second reference picture, the processing circuitry can determine asecond clipped MV by clipping the second MV such that an updated secondreference block is within the picture boundary of the second referencepicture. The second clipped MV points from the current block to theupdated second reference block, and the picture boundaries include thepicture boundary of the second reference picture.

In an embodiment, the current block is bi-predicted with an affine modeand includes plural subblocks. For each subblock in the pluralsubblocks, the processing circuitry can determine, for each region inthe respective subblock, an MV pair of the respective region using theaffine mode. The MV pair includes a respective first MV pointing fromthe region to the first reference region in a first reference subblockin the first reference block and a second MV pointing from the region toa second reference region in a second reference subblock that is in asecond reference block associated with a second reference picture. Thefirst reference block and the second reference block correspond to thecurrent block, and the first reference subblock and the second referencesubblock correspond to the respective subblock. The first referenceregion is in the first reference subblock in the first reference block,and the region in the current block is in a subblock of the pluralsubblocks corresponding to the first reference subblock. The firstreference region is outside the picture boundary of the first referencepicture. The processing circuitry can determine the first clipped MV byclipping the first MV where the first clipped MV points from the regionin the subblock to the updated first reference region.

Aspects of the disclosure also provide a non-transitorycomputer-readable storage medium storing a program executable by atleast one processor to perform the methods for video decoding.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1A is a schematic illustration of an exemplary subset of intraprediction modes.

FIG. 1B is an illustration of exemplary intra prediction directions.

FIG. 2 shows an example of a current block (201) and surroundingsamples.

FIG. 3 is a schematic illustration of an exemplary block diagram of acommunication system (300).

FIG. 4 is a schematic illustration of an exemplary block diagram of acommunication system (400).

FIG. 5 is a schematic illustration of an exemplary block diagram of adecoder.

FIG. 6 is a schematic illustration of an exemplary block diagram of anencoder.

FIG. 7 shows a block diagram of an exemplary encoder.

FIG. 8 shows a block diagram of an exemplary decoder.

FIG. 9 shows positions of spatial merge candidates according to anembodiment of the disclosure.

FIG. 10 shows candidate pairs that are considered for a redundancy checkof spatial merge candidates according to an embodiment of thedisclosure.

FIG. 11 shows exemplary motion vector scaling for a temporal mergecandidate.

FIG. 12 shows exemplary candidate positions for a temporal mergecandidate of a current coding unit.

FIG. 13 shows an example of an adaptive motion vector resolution (AMVR)shift value corresponding to a motion vector resolution (MVR).

FIGS. 14A-14B show exemplary modifications of motion vector differencesin an adaptive motion vector prediction (AMVP) mode and in an affineAMVP mode when an AMVR mode is enabled.

FIG. 15A shows an affine motion field of a block when a 4-parameteraffine model is used.

FIG. 15B shows an affine motion field of a block when a 6-parameteraffine model is used.

FIG. 16 shows an example of a sub-block based affine transformprediction.

FIG. 17 shows an example of determining a control point motion vector(CPMV) candidate in an affine merge list of a current CU.

FIG. 18 shows examples of spatial neighbors and a temporal neighbor of acurrent block.

FIG. 19 shows an example of a reference picture of a current block andreference blocks of the current block.

FIG. 20 shows a flow chart outlining an encoding process according to anembodiment of the disclosure.

FIG. 21 shows a flow chart outlining a decoding process according to anembodiment of the disclosure.

FIG. 22 is a schematic illustration of a computer system in accordancewith an embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 3 illustrates an exemplary block diagram of a communication system(300). The communication system (300) includes a plurality of terminaldevices that can communicate with each other, via, for example, anetwork (350). For example, the communication system (300) includes afirst pair of terminal devices (310) and (320) interconnected via thenetwork (350). In the FIG. 3 example, the first pair of terminal devices(310) and (320) performs unidirectional transmission of data. Forexample, the terminal device (310) may code video data (e.g., a streamof video pictures that are captured by the terminal device (310)) fortransmission to the other terminal device (320) via the network (350).The encoded video data can be transmitted in the form of one or morecoded video bitstreams. The terminal device (320) may receive the codedvideo data from the network (350), decode the coded video data torecover the video pictures and display video pictures according to therecovered video data. Unidirectional data transmission may be common inmedia serving applications and the like.

In another example, the communication system (300) includes a secondpair of terminal devices (330) and (340) that perform bidirectionaltransmission of coded video data, for example, during videoconferencing.For bidirectional transmission of data, in an example, each terminaldevice of the terminal devices (330) and (340) may code video data(e.g., a stream of video pictures that are captured by the terminaldevice) for transmission to the other terminal device of the terminaldevices (330) and (340) via the network (350). Each terminal device ofthe terminal devices (330) and (340) also may receive the coded videodata transmitted by the other terminal device of the terminal devices(330) and (340), and may decode the coded video data to recover thevideo pictures and may display video pictures at an accessible displaydevice according to the recovered video data.

In the example of FIG. 3 , the terminal devices (310), (320), (330) and(340) are respectively illustrated as servers, personal computers andsmart phones but the principles of the present disclosure may be not solimited. Embodiments of the present disclosure find application withlaptop computers, tablet computers, media players, and/or dedicatedvideo conferencing equipment. The network (350) represents any number ofnetworks that convey coded video data among the terminal devices (310),(320), (330) and (340), including for example wireline (wired) and/orwireless communication networks. The communication network (350) mayexchange data in circuit-switched and/or packet-switched channels.Representative networks include telecommunications networks, local areanetworks, wide area networks and/or the Internet. For the purposes ofthe present discussion, the architecture and topology of the network(350) may be immaterial to the operation of the present disclosureunless explained herein below.

FIG. 4 illustrates, as an example of an application for the disclosedsubject matter, a video encoder and a video decoder in a streamingenvironment. The disclosed subject matter can be equally applicable toother video enabled applications, including, for example, videoconferencing, digital TV, streaming services, storing of compressedvideo on digital media including CD, DVD, memory stick and the like, andso on.

A streaming system may include a capture subsystem (413), that caninclude a video source (401), for example a digital camera, creating forexample a stream of video pictures (402) that are uncompressed. In anexample, the stream of video pictures (402) includes samples that aretaken by the digital camera. The stream of video pictures (402),depicted as a bold line to emphasize a high data volume when compared toencoded video data (404) (or coded video bitstreams), can be processedby an electronic device (420) that includes a video encoder (403)coupled to the video source (401). The video encoder (403) can includehardware, software, or a combination thereof to enable or implementaspects of the disclosed subject matter as described in more detailbelow. The encoded video data (404) (or encoded video bitstream),depicted as a thin line to emphasize the lower data volume when comparedto the stream of video pictures (402), can be stored on a streamingserver (405) for future use. One or more streaming client subsystems,such as client subsystems (406) and (408) in FIG. 4 can access thestreaming server (405) to retrieve copies (407) and (409) of the encodedvideo data (404). A client subsystem (406) can include a video decoder(410), for example, in an electronic device (430). The video decoder(410) decodes the incoming copy (407) of the encoded video data andcreates an outgoing stream of video pictures (411) that can be renderedon a display (412) (e.g., display screen) or other rendering device (notdepicted). In some streaming systems, the encoded video data (404),(407), and (409) (e.g., video bitstreams) can be encoded according tocertain video coding/compression standards. Examples of those standardsinclude ITU-T Recommendation H.265. In an example, a video codingstandard under development is informally known as Versatile Video Coding(VVC). The disclosed subject matter may be used in the context of VVC.

It is noted that the electronic devices (420) and (430) can includeother components (not shown). For example, the electronic device (420)can include a video decoder (not shown) and the electronic device (430)can include a video encoder (not shown) as well.

FIG. 5 shows an exemplary block diagram of a video decoder (510). Thevideo decoder (510) can be included in an electronic device (530). Theelectronic device (530) can include a receiver (531) (e.g., receivingcircuitry). The video decoder (510) can be used in the place of thevideo decoder (410) in the FIG. 4 example.

The receiver (531) may receive one or more coded video sequences to bedecoded by the video decoder (510). In an embodiment, one coded videosequence is received at a time, where the decoding of each coded videosequence is independent from the decoding of other coded videosequences. The coded video sequence may be received from a channel(501), which may be a hardware/software link to a storage device whichstores the encoded video data. The receiver (531) may receive theencoded video data with other data, for example, coded audio data and/orancillary data streams, that may be forwarded to their respective usingentities (not depicted). The receiver (531) may separate the coded videosequence from the other data. To combat network jitter, a buffer memory(515) may be coupled in between the receiver (531) and an entropydecoder/parser (520) (“parser (520)” henceforth). In certainapplications, the buffer memory (515) is part of the video decoder(510). In others, it can be outside of the video decoder (510) (notdepicted). In still others, there can be a buffer memory (not depicted)outside of the video decoder (510), for example to combat networkjitter, and in addition another buffer memory (515) inside the videodecoder (510), for example to handle playout timing. When the receiver(531) is receiving data from a store/forward device of sufficientbandwidth and controllability, or from an isosynchronous network, thebuffer memory (515) may not be needed, or can be small. For use on besteffort packet networks such as the Internet, the buffer memory (515) maybe required, can be comparatively large and can be advantageously ofadaptive size, and may at least partially be implemented in an operatingsystem or similar elements (not depicted) outside of the video decoder(510).

The video decoder (510) may include the parser (520) to reconstructsymbols (521) from the coded video sequence. Categories of those symbolsinclude information used to manage operation of the video decoder (510),and potentially information to control a rendering device such as arender device (512) (e.g., a display screen) that is not an integralpart of the electronic device (530) but can be coupled to the electronicdevice (530), as shown in FIG. 5 . The control information for therendering device(s) may be in the form of Supplemental EnhancementInformation (SEI) messages or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (520) mayparse/entropy-decode the coded video sequence that is received. Thecoding of the coded video sequence can be in accordance with a videocoding technology or standard, and can follow various principles,including variable length coding, Huffman coding, arithmetic coding withor without context sensitivity, and so forth. The parser (520) mayextract from the coded video sequence, a set of subgroup parameters forat least one of the subgroups of pixels in the video decoder, based uponat least one parameter corresponding to the group. Subgroups can includeGroups of Pictures (GOPs), pictures, tiles, slices, macroblocks, CodingUnits (CUs), blocks, Transform Units (TUs), Prediction Units (PUs) andso forth. The parser (520) may also extract from the coded videosequence information such as transform coefficients, quantizer parametervalues, motion vectors, and so forth.

The parser (520) may perform an entropy decoding/parsing operation onthe video sequence received from the buffer memory (515), so as tocreate symbols (521).

Reconstruction of the symbols (521) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by subgroup controlinformation parsed from the coded video sequence by the parser (520).The flow of such subgroup control information between the parser (520)and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, the video decoder (510)can be conceptually subdivided into a number of functional units asdescribed below. In a practical implementation operating undercommercial constraints, many of these units interact closely with eachother and can, at least partly, be integrated into each other. However,for the purpose of describing the disclosed subject matter, theconceptual subdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit (551). Thescaler/inverse transform unit (551) receives a quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (521) from the parser (520). The scaler/inversetransform unit (551) can output blocks comprising sample values, thatcan be input into aggregator (555).

In some cases, the output samples of the scaler/inverse transform unit(551) can pertain to an intra coded block. The intra coded block is ablock that is not using predictive information from previouslyreconstructed pictures, but can use predictive information frompreviously reconstructed parts of the current picture. Such predictiveinformation can be provided by an intra picture prediction unit (552).In some cases, the intra picture prediction unit (552) generates a blockof the same size and shape of the block under reconstruction, usingsurrounding already reconstructed information fetched from the currentpicture buffer (558). The current picture buffer (558) buffers, forexample, partly reconstructed current picture and/or fully reconstructedcurrent picture. The aggregator (555), in some cases, adds, on a persample basis, the prediction information the intra prediction unit (552)has generated to the output sample information as provided by thescaler/inverse transform unit (551).

In other cases, the output samples of the scaler/inverse transform unit(551) can pertain to an inter coded, and potentially motion compensated,block. In such a case, a motion compensation prediction unit (553) canaccess reference picture memory (557) to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols (521) pertaining to the block, these samples can beadded by the aggregator (555) to the output of the scaler/inversetransform unit (551) (in this case called the residual samples orresidual signal) so as to generate output sample information. Theaddresses within the reference picture memory (557) from where themotion compensation prediction unit (553) fetches prediction samples canbe controlled by motion vectors, available to the motion compensationprediction unit (553) in the form of symbols (521) that can have, forexample X, Y, and reference picture components. Motion compensation alsocan include interpolation of sample values as fetched from the referencepicture memory (557) when sub-sample exact motion vectors are in use,motion vector prediction mechanisms, and so forth.

The output samples of the aggregator (555) can be subject to variousloop filtering techniques in the loop filter unit (556). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video sequence (alsoreferred to as coded video bitstream) and made available to the loopfilter unit (556) as symbols (521) from the parser (520). Videocompression can also be responsive to meta-information obtained duringthe decoding of previous (in decoding order) parts of the coded pictureor coded video sequence, as well as responsive to previouslyreconstructed and loop-filtered sample values.

The output of the loop filter unit (556) can be a sample stream that canbe output to the render device (512) as well as stored in the referencepicture memory (557) for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. For example, once a codedpicture corresponding to a current picture is fully reconstructed andthe coded picture has been identified as a reference picture (by, forexample, the parser (520)), the current picture buffer (558) can becomea part of the reference picture memory (557), and a fresh currentpicture buffer can be reallocated before commencing the reconstructionof the following coded picture.

The video decoder (510) may perform decoding operations according to apredetermined video compression technology or a standard, such as ITU-TRec. H.265. The coded video sequence may conform to a syntax specifiedby the video compression technology or standard being used, in the sensethat the coded video sequence adheres to both the syntax of the videocompression technology or standard and the profiles as documented in thevideo compression technology or standard. Specifically, a profile canselect certain tools as the only tools available for use under thatprofile from all the tools available in the video compression technologyor standard. Also necessary for compliance can be that the complexity ofthe coded video sequence is within bounds as defined by the level of thevideo compression technology or standard. In some cases, levels restrictthe maximum picture size, maximum frame rate, maximum reconstructionsample rate (measured in, for example megasamples per second), maximumreference picture size, and so on. Limits set by levels can, in somecases, be further restricted through Hypothetical Reference Decoder(HRD) specifications and metadata for HRD buffer management signaled inthe coded video sequence.

In an embodiment, the receiver (531) may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder (510) to properly decode the data and/or to moreaccurately reconstruct the original video data. Additional data can bein the form of, for example, temporal, spatial, or signal noise ratio(SNR) enhancement layers, redundant slices, redundant pictures, forwarderror correction codes, and so on.

FIG. 6 shows an exemplary block diagram of a video encoder (603). Thevideo encoder (603) is included in an electronic device (620). Theelectronic device (620) includes a transmitter (640) (e.g., transmittingcircuitry). The video encoder (603) can be used in the place of thevideo encoder (403) in the FIG. 4 example.

The video encoder (603) may receive video samples from a video source(601) (that is not part of the electronic device (620) in the FIG. 6example) that may capture video image(s) to be coded by the videoencoder (603). In another example, the video source (601) is a part ofthe electronic device (620).

The video source (601) may provide the source video sequence to be codedby the video encoder (603) in the form of a digital video sample streamthat can be of any suitable bit depth (for example: 8 bit, 10 bit, 12bit, . . . ), any colorspace (for example, BT.601 Y CrCB, RGB, . . . ),and any suitable sampling structure (for example Y CrCb 4:2:0, Y CrCb4:4:4). In a media serving system, the video source (601) may be astorage device storing previously prepared video. In a videoconferencingsystem, the video source (601) may be a camera that captures local imageinformation as a video sequence. Video data may be provided as aplurality of individual pictures that impart motion when viewed insequence. The pictures themselves may be organized as a spatial array ofpixels, wherein each pixel can comprise one or more samples depending onthe sampling structure, color space, etc. in use. A person skilled inthe art can readily understand the relationship between pixels andsamples. The description below focuses on samples.

According to an embodiment, the video encoder (603) may code andcompress the pictures of the source video sequence into a coded videosequence (643) in real time or under any other time constraints asrequired. Enforcing appropriate coding speed is one function of acontroller (650). In some embodiments, the controller (650) controlsother functional units as described below and is functionally coupled tothe other functional units. The coupling is not depicted for clarity.Parameters set by the controller (650) can include rate control relatedparameters (picture skip, quantizer, lambda value of rate-distortionoptimization techniques, . . . ), picture size, group of pictures (GOP)layout, maximum motion vector search range, and so forth. The controller(650) can be configured to have other suitable functions that pertain tothe video encoder (603) optimized for a certain system design.

In some embodiments, the video encoder (603) is configured to operate ina coding loop. As an oversimplified description, in an example, thecoding loop can include a source coder (630) (e.g., responsible forcreating symbols, such as a symbol stream, based on an input picture tobe coded, and a reference picture(s)), and a (local) decoder (633)embedded in the video encoder (603). The decoder (633) reconstructs thesymbols to create the sample data in a similar manner as a (remote)decoder also would create. The reconstructed sample stream (sample data)is input to the reference picture memory (634). As the decoding of asymbol stream leads to bit-exact results independent of decoder location(local or remote), the content in the reference picture memory (634) isalso bit exact between the local encoder and remote encoder. In otherwords, the prediction part of an encoder “sees” as reference picturesamples exactly the same sample values as a decoder would “see” whenusing prediction during decoding. This fundamental principle ofreference picture synchronicity (and resulting drift, if synchronicitycannot be maintained, for example because of channel errors) is used insome related arts as well.

The operation of the “local” decoder (633) can be the same as of a“remote” decoder, such as the video decoder (510), which has alreadybeen described in detail above in conjunction with FIG. 5 . Brieflyreferring also to FIG. 5 , however, as symbols are available andencoding/decoding of symbols to a coded video sequence by an entropycoder (645) and the parser (520) can be lossless, the entropy decodingparts of the video decoder (510), including the buffer memory (515), andparser (520) may not be fully implemented in the local decoder (633).

In an embodiment, a decoder technology except the parsing/entropydecoding that is present in a decoder is present, in an identical or asubstantially identical functional form, in a corresponding encoder.Accordingly, the disclosed subject matter focuses on decoder operation.The description of encoder technologies can be abbreviated as they arethe inverse of the comprehensively described decoder technologies. Incertain areas a more detail description is provided below.

During operation, in some examples, the source coder (630) may performmotion compensated predictive coding, which codes an input picturepredictively with reference to one or more previously coded picture fromthe video sequence that were designated as “reference pictures.” In thismanner, the coding engine (632) codes differences between pixel blocksof an input picture and pixel blocks of reference picture(s) that may beselected as prediction reference(s) to the input picture.

The local video decoder (633) may decode coded video data of picturesthat may be designated as reference pictures, based on symbols createdby the source coder (630). Operations of the coding engine (632) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 6 ), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (633) replicates decodingprocesses that may be performed by the video decoder on referencepictures and may cause reconstructed reference pictures to be stored inthe reference picture memory (634). In this manner, the video encoder(603) may store copies of reconstructed reference pictures locally thathave common content as the reconstructed reference pictures that will beobtained by a far-end video decoder (absent transmission errors).

The predictor (635) may perform prediction searches for the codingengine (632). That is, for a new picture to be coded, the predictor(635) may search the reference picture memory (634) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(635) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (635), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (634).

The controller (650) may manage coding operations of the source coder(630), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (645). The entropy coder (645)translates the symbols as generated by the various functional units intoa coded video sequence, by applying lossless compression to the symbolsaccording to technologies such as Huffman coding, variable lengthcoding, arithmetic coding, and so forth.

The transmitter (640) may buffer the coded video sequence(s) as createdby the entropy coder (645) to prepare for transmission via acommunication channel (660), which may be a hardware/software link to astorage device which would store the encoded video data. The transmitter(640) may merge coded video data from the video encoder (603) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (650) may manage operation of the video encoder (603).During coding, the controller (650) may assign to each coded picture acertain coded picture type, which may affect the coding techniques thatmay be applied to the respective picture. For example, pictures oftenmay be assigned as one of the following picture types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other picture in the sequence as a source ofprediction. Some video codecs allow for different types of intrapictures, including, for example Independent Decoder Refresh (“IDR”)Pictures. A person skilled in the art is aware of those variants of Ipictures and their respective applications and features.

A predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A bi-directionally predictive picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded predictively, viaspatial prediction or via temporal prediction with reference to onepreviously coded reference picture. Blocks of B pictures may be codedpredictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video encoder (603) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video encoder (603) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter (640) may transmit additional datawith the encoded video. The source coder (630) may include such data aspart of the coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, SEI messages, VUI parameter setfragments, and so on.

A video may be captured as a plurality of source pictures (videopictures) in a temporal sequence. Intra-picture prediction (oftenabbreviated to intra prediction) makes use of spatial correlation in agiven picture, and inter-picture prediction makes uses of the (temporalor other) correlation between the pictures. In an example, a specificpicture under encoding/decoding, which is referred to as a currentpicture, is partitioned into blocks. When a block in the current pictureis similar to a reference block in a previously coded and still bufferedreference picture in the video, the block in the current picture can becoded by a vector that is referred to as a motion vector. The motionvector points to the reference block in the reference picture, and canhave a third dimension identifying the reference picture, in casemultiple reference pictures are in use.

In some embodiments, a bi-prediction technique can be used in theinter-picture prediction. According to the bi-prediction technique, tworeference pictures, such as a first reference picture and a secondreference picture that are both prior in decoding order to the currentpicture in the video (but may be in the past and future, respectively,in display order) are used. A block in the current picture can be codedby a first motion vector that points to a first reference block in thefirst reference picture, and a second motion vector that points to asecond reference block in the second reference picture. The block can bepredicted by a combination of the first reference block and the secondreference block.

Further, a merge mode technique can be used in the inter-pictureprediction to improve coding efficiency.

According to some embodiments of the disclosure, predictions, such asinter-picture predictions and intra-picture predictions, are performedin the unit of blocks. For example, according to the HEVC standard, apicture in a sequence of video pictures is partitioned into coding treeunits (CTU) for compression, the CTUs in a picture have the same size,such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. In general, a CTUincludes three coding tree blocks (CTBs), which are one luma CTB and twochroma CTBs. Each CTU can be recursively quadtree split into one ormultiple coding units (CUs). For example, a CTU of 64×64 pixels can besplit into one CU of 64×64 pixels, or 4 CUs of 32×32 pixels, or 16 CUsof 16×16 pixels. In an example, each CU is analyzed to determine aprediction type for the CU, such as an inter prediction type or an intraprediction type. The CU is split into one or more prediction units (PUs)depending on the temporal and/or spatial predictability. Generally, eachPU includes a luma prediction block (PB), and two chroma PBs. In anembodiment, a prediction operation in coding (encoding/decoding) isperformed in the unit of a prediction block. Using a luma predictionblock as an example of a prediction block, the prediction block includesa matrix of values (e.g., luma values) for pixels, such as 8×8 pixels,16×16 pixels, 8×16 pixels, 16×8 pixels, and the like.

FIG. 7 shows an exemplary diagram of a video encoder (703). The videoencoder (703) is configured to receive a processing block (e.g., aprediction block) of sample values within a current video picture in asequence of video pictures, and encode the processing block into a codedpicture that is part of a coded video sequence. In an example, the videoencoder (703) is used in the place of the video encoder (403) in theFIG. 4 example.

In an HEVC example, the video encoder (703) receives a matrix of samplevalues for a processing block, such as a prediction block of 8×8samples, and the like. The video encoder (703) determines whether theprocessing block is best coded using intra mode, inter mode, orbi-prediction mode using, for example, rate-distortion optimization.When the processing block is to be coded in intra mode, the videoencoder (703) may use an intra prediction technique to encode theprocessing block into the coded picture; and when the processing blockis to be coded in inter mode or bi-prediction mode, the video encoder(703) may use an inter prediction or bi-prediction technique,respectively, to encode the processing block into the coded picture. Incertain video coding technologies, merge mode can be an inter pictureprediction submode where the motion vector is derived from one or moremotion vector predictors without the benefit of a coded motion vectorcomponent outside the predictors. In certain other video codingtechnologies, a motion vector component applicable to the subject blockmay be present. In an example, the video encoder (703) includes othercomponents, such as a mode decision module (not shown) to determine themode of the processing blocks.

In the FIG. 7 example, the video encoder (703) includes an inter encoder(730), an intra encoder (722), a residue calculator (723), a switch(726), a residue encoder (724), a general controller (721), and anentropy encoder (725) coupled together as shown in FIG. 7 .

The inter encoder (730) is configured to receive the samples of thecurrent block (e.g., a processing block), compare the block to one ormore reference blocks in reference pictures (e.g., blocks in previouspictures and later pictures), generate inter prediction information(e.g., description of redundant information according to inter encodingtechnique, motion vectors, merge mode information), and calculate interprediction results (e.g., predicted block) based on the inter predictioninformation using any suitable technique. In some examples, thereference pictures are decoded reference pictures that are decoded basedon the encoded video information.

The intra encoder (722) is configured to receive the samples of thecurrent block (e.g., a processing block), in some cases compare theblock to blocks already coded in the same picture, generate quantizedcoefficients after transform, and in some cases also generate intraprediction information (e.g., an intra prediction direction informationaccording to one or more intra encoding techniques). In an example, theintra encoder (722) also calculates intra prediction results (e.g.,predicted block) based on the intra prediction information and referenceblocks in the same picture.

The general controller (721) is configured to determine general controldata and control other components of the video encoder (703) based onthe general control data. In an example, the general controller (721)determines the mode of the block, and provides a control signal to theswitch (726) based on the mode. For example, when the mode is the intramode, the general controller (721) controls the switch (726) to selectthe intra mode result for use by the residue calculator (723), andcontrols the entropy encoder (725) to select the intra predictioninformation and include the intra prediction information in thebitstream; and when the mode is the inter mode, the general controller(721) controls the switch (726) to select the inter prediction resultfor use by the residue calculator (723), and controls the entropyencoder (725) to select the inter prediction information and include theinter prediction information in the bitstream.

The residue calculator (723) is configured to calculate a difference(residue data) between the received block and prediction resultsselected from the intra encoder (722) or the inter encoder (730). Theresidue encoder (724) is configured to operate based on the residue datato encode the residue data to generate the transform coefficients. In anexample, the residue encoder (724) is configured to convert the residuedata from a spatial domain to a frequency domain, and generate thetransform coefficients. The transform coefficients are then subject toquantization processing to obtain quantized transform coefficients. Invarious embodiments, the video encoder (703) also includes a residuedecoder (728). The residue decoder (728) is configured to performinverse-transform, and generate the decoded residue data. The decodedresidue data can be suitably used by the intra encoder (722) and theinter encoder (730). For example, the inter encoder (730) can generatedecoded blocks based on the decoded residue data and inter predictioninformation, and the intra encoder (722) can generate decoded blocksbased on the decoded residue data and the intra prediction information.The decoded blocks are suitably processed to generate decoded picturesand the decoded pictures can be buffered in a memory circuit (not shown)and used as reference pictures in some examples.

The entropy encoder (725) is configured to format the bitstream toinclude the encoded block. The entropy encoder (725) is configured toinclude various information in the bitstream according to a suitablestandard, such as the HEVC standard. In an example, the entropy encoder(725) is configured to include the general control data, the selectedprediction information (e.g., intra prediction information or interprediction information), the residue information, and other suitableinformation in the bitstream. Note that, according to the disclosedsubject matter, when coding a block in the merge submode of either intermode or bi-prediction mode, there is no residue information.

FIG. 8 shows an exemplary diagram of a video decoder (810). The videodecoder (810) is configured to receive coded pictures that are part of acoded video sequence, and decode the coded pictures to generatereconstructed pictures. In an example, the video decoder (810) is usedin the place of the video decoder (410) in the FIG. 4 example.

In the FIG. 8 example, the video decoder (810) includes an entropydecoder (871), an inter decoder (880), a residue decoder (873), areconstruction module (874), and an intra decoder (872) coupled togetheras shown in FIG. 8 .

The entropy decoder (871) can be configured to reconstruct, from thecoded picture, certain symbols that represent the syntax elements ofwhich the coded picture is made up. Such symbols can include, forexample, the mode in which a block is coded (such as, for example, intramode, inter mode, bi-predicted mode, the latter two in merge submode oranother submode) and prediction information (such as, for example, intraprediction information or inter prediction information) that canidentify certain sample or metadata that is used for prediction by theintra decoder (872) or the inter decoder (880), respectively. Thesymbols can also include residual information in the form of, forexample, quantized transform coefficients, and the like. In an example,when the prediction mode is inter or bi-predicted mode, the interprediction information is provided to the inter decoder (880); and whenthe prediction type is the intra prediction type, the intra predictioninformation is provided to the intra decoder (872). The residualinformation can be subject to inverse quantization and is provided tothe residue decoder (873).

The inter decoder (880) is configured to receive the inter predictioninformation, and generate inter prediction results based on the interprediction information.

The intra decoder (872) is configured to receive the intra predictioninformation, and generate prediction results based on the intraprediction information.

The residue decoder (873) is configured to perform inverse quantizationto extract de-quantized transform coefficients, and process thede-quantized transform coefficients to convert the residual informationfrom the frequency domain to the spatial domain. The residue decoder(873) may also require certain control information (to include theQuantizer Parameter (QP)), and that information may be provided by theentropy decoder (871) (data path not depicted as this may be low volumecontrol information only).

The reconstruction module (874) is configured to combine, in the spatialdomain, the residual information as output by the residue decoder (873)and the prediction results (as output by the inter or intra predictionmodules as the case may be) to form a reconstructed block, that may bepart of the reconstructed picture, which in turn may be part of thereconstructed video. It is noted that other suitable operations, such asa deblocking operation and the like, can be performed to improve thevisual quality.

It is noted that the video encoders (403), (603), and (703), and thevideo decoders (410), (510), and (810) can be implemented using anysuitable technique. In an embodiment, the video encoders (403), (603),and (703), and the video decoders (410), (510), and (810) can beimplemented using one or more integrated circuits. In anotherembodiment, the video encoders (403), (603), and (603), and the videodecoders (410), (510), and (810) can be implemented using one or moreprocessors that execute software instructions.

Various inter prediction modes can be used in VVC. For aninter-predicted CU, motion parameters can include MV(s), one or morereference picture indices, a reference picture list usage index, andadditional information for certain coding features to be used forinter-predicted sample generation. A motion parameter can be signaledexplicitly or implicitly. When a CU is coded with a skip mode, the CUcan be associated with a PU and can have no significant residualcoefficients, no coded motion vector delta or MV difference (e.g., MVD)or a reference picture index. A merge mode can be specified where themotion parameters for the current CU are obtained from neighboringCU(s), including spatial and/or temporal candidates, and optionallyadditional information such as introduced in VVC. The merge mode can beapplied to an inter-predicted CU, not only for skip mode. In an example,an alternative to the merge mode is the explicit transmission of motionparameters, where MV(s), a corresponding reference picture index foreach reference picture list and a reference picture list usage flag andother information are signaled explicitly per CU.

In an embodiment, such as in VVC, VVC Test model (VTM) referencesoftware includes one or more refined inter prediction coding tools thatinclude: an extended merge prediction, a merge motion vector difference(MMVD) mode, an adaptive motion vector prediction (AMVP) mode withsymmetric MVD signaling, an affine motion compensated prediction, asubblock-based temporal motion vector prediction (SbTMVP), an adaptivemotion vector resolution (AMVR), a motion field storage ( 1/16th lumasample MV storage and 8×8 motion field compression), a bi-predictionwith CU-level weights (BCW), a bi-directional optical flow (BDOF), aprediction refinement using optical flow (PROF), a decoder side motionvector refinement (DMVR), a combined inter and intra prediction (CIIP),a geometric partitioning mode (GPM), and the like. Inter predictions andrelated methods are described in details below.

Extended merge prediction can be used in some examples. In an example,such as in VTM4, a merge candidate list is constructed by including thefollowing five types of candidates in order: spatial motion vectorpredictor(s) (MVP(s)) from spatial neighboring CU(s), temporal MVP(s)from collocated CU(s), history-based MVP(s) from a first-in-first-out(FIFO) table, pairwise average MVP(s), and zero MV(s).

A size of the merge candidate list can be signaled in a slice header. Inan example, the maximum allowed size of the merge candidate list is 6 inVTM4. For each CU coded in the merge mode, an index (e.g., a mergeindex) of a best merge candidate can be encoded using truncated unarybinarization (TU). The first bin of the merge index can be coded withcontext (e.g., context-adaptive binary arithmetic coding (CABAC)) and abypass coding can be used for other bins.

Some examples of a generation process of each category of mergecandidates are provided below. In an embodiment, spatial candidate(s)are derived as follows. The derivation of spatial merge candidates inVVC can be identical to that in HEVC. In an example, a maximum of fourmerge candidates are selected among candidates located in positionsdepicted in FIG. 9 . FIG. 9 shows positions of spatial merge candidatesaccording to an embodiment of the disclosure. Referring to FIG. 9 , anorder of derivation is B1, A1, B0, A0, and B2. The position B2 isconsidered only when any CU of positions A0, B0, B1, and A1 is notavailable (e.g. because the CU belongs to another slice or another tile)or is intra coded. After a candidate at the position A1 is added, theaddition of the remaining candidates is subject to a redundancy checkwhich ensures that candidates with same motion information are excludedfrom the candidate list so that coding efficiency is improved.

To reduce computational complexity, not all possible candidate pairs areconsidered in the mentioned redundancy check. Instead, only pairs linkedwith an arrow in FIG. 10 are considered and a candidate is only added tothe candidate list if the corresponding candidate used for theredundancy check does not have the same motion information. FIG. 10shows candidate pairs that are considered for a redundancy check ofspatial merge candidates according to an embodiment of the disclosure.Referring to FIG. 10 , the pairs linked with respective arrows includeA1 and B1, A1 and A0, A1 and B2, B1 and B0, and B1 and B2. Thus,candidates at the positions B1, A0, and/or B2 can be compared with thecandidate at the position A1, and candidates at the positions B0 and/orB2 can be compared with the candidate at the position B1.

In an embodiment, temporal candidate(s) are derived as follows. In anexample, only one temporal merge candidate is added to the candidatelist. FIG. 11 shows exemplary motion vector scaling for a temporal mergecandidate. To derive the temporal merge candidate of a current CU (1111)in a current picture (1101), a scaled MV (1121) (e.g., shown by a dottedline in FIG. 11 ) can be derived based on a co-located CU (1112)belonging to a co-located reference picture (1104). A reference picturelist used to derive the co-located CU (1112) can be explicitly signaledin a slice header. The scaled MV (1121) for the temporal merge candidatecan be obtained as shown by the dotted line in FIG. 11 . The scaled MV(1121) can be scaled from the MV of the co-located CU (1112) usingpicture order count (POC) distances tb and td. The POC distance tb canbe defined to be the POC difference between a current reference picture(1102) of the current picture (1101) and the current picture (1101). ThePOC distance td can be defined to be the POC difference between theco-located reference picture (1104) of the co-located picture (1103) andthe co-located picture (1103). A reference picture index of the temporalmerge candidate can be set to zero.

FIG. 12 shows exemplary candidate positions (e.g., C0 and C1) for atemporal merge candidate of a current CU. A position for the temporalmerge candidate can be selected between the candidate positions C0 andC1. The candidate position C0 is located at a bottom-right corner of aco-located CU (1210) of the current CU. The candidate position C1 islocated at a center of the co-located CU (1210) of the current CU. If aCU at the candidate position C0 is not available, is intra coded, or isoutside of a current row of CTUs, the candidate position C1 is used toderive the temporal merge candidate. Otherwise, for example, the CU atthe candidate position C0 is available, intra coded, and in the currentrow of CTUs, the candidate position C0 is used to derive the temporalmerge candidate.

An adaptive motion vector resolution (AMVR) mode can be used invideo/image coding, such as in VVC. In some technologies, such as thevideo coding standards HEVC and AVC/H.264, a fixed motion vectorresolution (MVR) of a quarter (¼) luma samples (or ¼-pel) is used. Ingeneral, an optimum trade-off between a displacement vector rate and aprediction error rate is chosen to optimize the rate-distortion. Inrelated technologies, such as VVC, the AMVR mode is enabled where an MVRcan be selected, for example, at a coding block level from a pluralityof MVRs, and thus to trade off a bit rate for fidelity of signalingmotion parameters. The AMVR mode can be signaled at the coding blocklevel, for example, if at least one component of an MVD is not equal tozero. A motion vector predictor (MVP) can be rounded to the given MVRsuch that a resulting MV (e.g., a sum of the MVP and the MVD) can fallon a grid of the given MVR.

FIG. 13 shows an example of an Amvr shift value (e.g., AmvrShift)corresponding to a resolution (e.g., an MVR). For each given resolution(e.g., the MVR), the corresponding Amvr shift value (e.g., AmvrShift)indicates a shifting operation (e.g., a left shifting operation). Forexample, the AmvrShift is defined to specify the MVR of the MVD with aleft shifting operation, and a number of bits that is shifted isindicated by the AmvrShift.

In some examples, a flag, such as an AMVR flag (e.g., amvr_flag)specifies a resolution (e.g., an MVR) of an MVD. In an example, the AMVRflag (e.g., the amvr_flag) being equal to 0 specifies that the MVR ofthe MVD is ¼ luma samples (¼-pel). Referring to FIG. 13 , an MVR of¼-pel corresponds to the left shifting operation of 2 bits (e.g.,AmvrShift being 2 bits).

The AMVR flag (e.g., amvr_flag) being equal to 1 specifies that the MVRof the MVD is further specified by addition information such as an index(e.g., an AMVR precision index or denoted as amvr_precision_idx in FIG.13 ) and/or the prediction mode. Referring to FIG. 13 , the predictionmode can be an affine prediction mode or an affine mode indicated by theinter affine flag, an IBC mode indicated by a parameter mode IBC, or aninter prediction mode that is neither the affine prediction mode nor theIBC mode. For example, the inter prediction mode is whole block-basedinter prediction.

For example, the coding block is predicted with the AMVP mode and theAMVR flag (e.g., amvr_flag) is 1, and thus the MVR is ½ luma samples(½-Pel), 1 Luma sample (1-pel), or 4 luma samples (4-pel) when the AMVRprecision index is 0, 1, or 2, respectively when the inter predictionmode (e.g., the whole block-based inter prediction) is neither theaffine prediction mode nor the IBC mode. In an example, ½-pel, 1-pel, or4-pel corresponds to an AmvrShift of 3, 4, or 6 bits.

The given MVDs, denoted as MvdL0 and MvdL1 in the AMVP mode or denotedas MvdCpL0, and MvdCpL1 in the affine AMVP mode, can be modified asshown in FIG. 14A or FIG. 14B when the AMVR mode is enabled.

In some examples, a translation motion model is applied for motioncompensation prediction (MCP). However, the translational motion modelmay not be suitable for modeling other types of motions, such as zoomin/out, rotation, perspective motions, and the other irregular motions.In some embodiments, a block-based affine transform motion compensationprediction is applied. In FIG. 15A, an affine motion field of a block isdescribed by two control point motion vectors (CPMVs), CPMV0 and CPMV1,of two control points (CPs), CP0 and CP1 when a 4-parameter affine modelis used. In FIG. 15B, an affine motion field of a block is described bythree CPMVs, CPMV0, CPMV1 and CPMV3, of CPs, CP0, CP1, and CP2 when a6-parameter affine model is used.

For a 4-parameter affine motion model, a motion vector at a samplelocation (x, y) in a block is derived as:

$\begin{matrix}\{ \begin{matrix}{{mv}_{x} = {{\frac{{mv}_{1x} - {mv}_{0x}}{W}x} + {\frac{{mv}_{1y} - {mv}_{0y}}{W}y} + {mv}_{0x}}} \\{{mv}_{y} = {{\frac{{mv}_{1y} - {mv}_{0y}}{W}x} + {\frac{{mv}_{1y} - {mv}_{0x}}{W}y} + {mv}_{0y}}}\end{matrix}  & {{Eq}.1}\end{matrix}$

For a 6-parameter affine motion model, a motion vector at samplelocation (x, y) in a block is derived as:

$\begin{matrix}\{ \begin{matrix}{{mv}_{x} = {{\frac{{mv}_{1x} - {mv}_{0x}}{W}x} + {\frac{{mv}_{2x} - {mv}_{0x}}{H}y} + {mv}_{0x}}} \\{{mv}_{y} = {{\frac{{mv}_{1y} - {mv}_{0y}}{W}x} + {\frac{{mv}_{2y} - {mv}_{0y}}{H}y} + {mv}_{0y}}}\end{matrix}  & {{Eq}.2}\end{matrix}$

In Eqs. 1-2, (mv_(0x), mv_(0y)) is a motion vector of the top-leftcorner control point, (mv_(1x), mv_(1y)) is motion vector of thetop-right corner control point, and (mv_(2x), mv_(2y)) is motion vectorof the bottom-left corner control point. In addition, the coordinate (x,y) is with respect to the top-left corner of the respective block, and Wand H denotes the width and height of the respective block.

In order to simplify the motion compensation prediction, a sub-blockbased affine transform prediction is applied in some embodiments. Forexample, in FIG. 16 , the 4-parameter affine motion model is used, andtwo CPMVs, {right arrow over (v₀)} and {right arrow over (v₁)}, aredetermined. To derive a motion vector of each 4×4 (samples) lumasub-block (1602) partitioned from the current block (1610), a motionvector (1601) of the center sample of each sub-block (1602) iscalculated according to Eq. 1, and rounded to a 1/16 fraction accuracy.Then, motion compensation interpolation filters are applied to generatea prediction of each sub-block (1602) with the derived motion vector(1601). The sub-block size of chroma-components is set to be 4×4. A MVof a 4×4 chroma sub-block is calculated as the average of the MVs of thefour corresponding 4×4 luma sub-blocks.

Similar to translational motion inter prediction, two affine motioninter prediction modes, affine merge mode and affine AMVP mode, areemployed in some embodiments.

In some embodiments, an affine merge mode can be applied for CUs withboth width and height larger than or equal to 8. Affine merge candidatesof a current CU can be generated based on motion information of spatialneighboring CUs. There can be up to five affine merge candidates and anindex is signaled to indicate the one to be used for the current CU. Forexample, the following three types of affine merge candidates are usedto form an affine merge candidate list:

-   -   (i) Inherited affine merge candidates that are extrapolated from        CPMVs of the neighbor CUs;    -   (ii) Constructed affine merge candidates that are derived using        the translational MVs of the neighbor CUs; and    -   (iii) Zero MVs.

In some embodiments, there can be at most two inherited affinecandidates which are derived from affine motion models of theneighboring blocks, one from left neighboring CUs and one from aboveneighboring CUs. The candidate blocks, for example, can be located atpositions shown in FIG. 9 . For the left predictor, the scan order isA0>A1, and for the above predictor, the scan order is B0>B1>B2. Only thefirst inherited candidate from each side is selected. No pruning checkis performed between two inherited candidates.

When a neighboring affine CU is identified, CPMVs of the identifiedneighboring affine CU are used to derive a CPMV candidate in the affinemerge list of the current CU. As shown in FIG. 17 , a neighbor leftbottom block A of a current CU (1710) is coded in an affine mode. Motionvectors, {right arrow over (v₂)}, {right arrow over (v₃)} and {rightarrow over (v₄)} of the top left corner, above right corner and leftbottom corner of a CU (1720) which contains the block A are attained.When block A is coded with a 4-parameter affine model, two CPMVs {rightarrow over (v₀)} and {right arrow over (v₁)} of the current CU (1710)are calculated according {right arrow over (v₂)}, and {right arrow over(v₃)}. In case that block A is coded with 6-parameter affine model,three CPMVs (not shown) of the current CU are calculated according to{right arrow over (v₂)}, {right arrow over (v₃)} and {right arrow over(v₄)}.

Constructed affine candidates are constructed by combining neighbortranslational motion information of each control point. The motioninformation for the control points is derived from specified spatialneighbors and temporal neighbor shown in FIG. 18 . CPMVk (k=1, 2, 3, 4)represents the k-th control point. For CPMV1, the B2>B3>A2 blocks arechecked in order and the MV of the first available block is used. ForCPMV2, the B1>B0 blocks are checked and for CPMV3, the A1>A0 blocks arechecked. A TMVP at block T is used as CPMV4 if available.

After MVs of four control points are attained, affine merge candidatesare constructed based on that motion information. The followingcombinations of control point MVs are used to construct in order:{CPMV1, CPMV2, CPMV3}, {CPMV1, CPMV2, CPMV4}, {CPMV1, CPMV3, CPMV4},{CPMV2, CPMV3, CPMV4}, {CPMV1, CPMV2}, {CPMV1, CPMV3}.

The combination of 3 CPMVs constructs a 6-parameter affine mergecandidate and the combination of 2 CPMVs constructs a 4-parameter affinemerge candidate. To avoid a motion scaling process, if the referenceindices of control points are different, the related combination ofcontrol point MVs is discarded.

After inherited affine merge candidates and constructed affine mergecandidates are checked, if the list is still not full, zero MVs areinserted to the end of the merge candidate list.

In some embodiments, affine AMVP mode can be applied for CUs with bothwidth and height larger than or equal to 16. An affine flag in CU levelis signaled in the bitstream to indicate whether affine AMVP mode isused and then another flag is signaled to indicate whether 4-parameteraffine or 6-parameter affine is used. A difference of the CPMVs ofcurrent CU and their predictors is signaled in the bitstream. An affineAVMP candidate list size is 2, and can be generated by using thefollowing four types of CPVM candidate in order:

-   -   (i) Inherited affine AMVP candidates that are extrapolated from        the CPMVs of the neighbor CUs;    -   (ii) Constructed affine AMVP candidates that are derived using        the translational MVs of the neighbor CUs;    -   (iii) Translational MVs from neighboring CUs; and    -   (iv) Zero MVs.

The checking order of inherited affine AMVP candidates is similar to thechecking order of inherited affine merge candidates in an example. Thedifference is that, for AVMP candidate, the affine CU that has the samereference picture as in current block is considered. No pruning processis applied when inserting an inherited affine motion predictor into thecandidate list.

Constructed AMVP candidate is derived from the specified spatialneighbors shown in FIG. 18 . A same checking order is used as done inaffine merge candidate construction. In addition, a reference pictureindex of a neighboring block is also checked. The first block in thechecking order that is inter coded and has the same reference picture asin current CUs is used. When the current CU is coded with a 4-parameteraffine model, and CPMV0 and CPMV1 are both available, the availableCPMVs are added as one candidate in the affine AMVP list. When thecurrent CU is coded with 6-parameter affine mode, and all three CPMVs(CPMV0, CPMV1, and CPMV2) are available, the available CPMVs are addedas one candidate in the affine AMVP list. Otherwise, constructed AMVPcandidates are set as unavailable.

If affine AMVP list candidates are still less than 2 after inheritedaffine AMVP candidates and constructed AMVP candidate are checked,translational motion vectors neighboring the control points will beadded to predict all control point MVs of the current CU, whenavailable. Finally, zero MVs are used to fill the affine AMVP list ifthe affine AMVP list is still not full.

In related technologies, such as in VVC and ECM, an MV can point to areference block outside a picture boundary or a frame boundary in aninter prediction mode (e.g., a uni-prediction mode or a bi-predictionmode). For example, one or more reference samples of the reference blockpointed to by the MV are located outside the picture boundary of areference picture. In some embodiments, an inter predictor (e.g., areference block in the uni-prediction mode or a bi-predictor based on afirst reference block and a second reference block for the bi-predictionmode) may not predict a current block accurately or efficiently when atleast one MV exceeds the frame boundary.

FIG. 19 shows an example of a reference picture (1901) (shaded in gray)of a current block (not shown) and reference blocks (1911)-(1914) of thecurrent block. A picture boundary or a frame boundary of the referencepicture (1901) can be determined by four corners C1-C4 of the referencepicture (1901). The four corners C1-C4 are a top-left corner C1, atop-right corner C2, a bottom-left corner C3, and a bottom-right cornerC4.

In FIG. 19 , the reference block (1911) is within the shaded area. Thereference block (1911) is within the reference picture (1901) or withinthe picture boundary of the reference picture (1901) when each referencesample in the reference block (1911) is within the reference picture(1901). The reference block (1911) has a rectangular shape, and fourcorners D1-D4 of the reference block (1911) is within the referencepicture (1901).

A reference block is outside the reference picture (1901) or outside thepicture boundary of the reference picture (1901) when at least onereference sample in the reference block is outside the reference picture(1901). For example, the reference block (1911) is outside the shadedarea. The reference block (1912) is outside the reference picture (1901)or outside the picture boundary of the reference picture (1901). Fourcorners E1-E4 of the reference block (1912) are outside the referencepicture (1901).

The reference block (1913) is partially outside the shaded area. Acorner F1 of the reference block (1913) is inside the reference picture(1901), and corners F2-F4 are outside the reference picture (1901). Thereference block (1913) is outside the reference picture (1901) oroutside the picture boundary of the reference picture (1901).

A current block in a current picture can be coded in the interprediction mode. The current block can be coded based on one or morereference blocks of the current block that are associated withrespective one or more reference pictures (e.g., (i) a first referencepicture or (ii) the first reference picture and a second referencepicture). According to an embodiment of the disclosure, motioninformation of the current block can be constrained. A motioninformation constraint of the current block can indicate that the one ormore reference blocks are within the respective one or more referencepictures, that is, the one or more reference blocks are within pictureboundaries of the respective one or more reference pictures. The motioninformation constraint can be pre-determined and agreed between anencoder and a decoder. The motion information constraint can be sent(e.g., signaled) to a decoder.

In an example, the current block is coded based on a first referenceblock associated with the first reference picture in the uni-predictionmode. The motion information constraint of the current block canindicate that the first reference block is within the first referencepicture. In an embodiment, the first reference block is within the firstreference picture when each first reference sample in the firstreference block is within the first reference picture (e.g., within apicture boundary of the first reference picture).

In an example, the current block is coded based on the first referenceblock associated with the first reference picture and a second referenceblock associated with the second reference picture in the bi-predictionmode. The motion information constraint of the current block canindicate that the first reference block is within the first referencepicture and the second reference block is within the second referencepicture.

In an embodiment, the current block is coded with a non-merge mode, suchas the AMVP mode. An MV (e.g., a final MV) of the current block can bedetermined (e.g., derived) from an MVP and an MVD at a given AMVRresolution. For example, the MV is a sum of the MVP and the MVD. The MVPcan be determined based on an index (e.g., an MVP index) and an MVPcandidate list of the current block. The motion information constraint(e.g., an MV constraint) for the non-merge mode can indicate that the MV(e.g., the final MV) cannot point out of a picture boundary of areference picture, for example, a reference block pointed to by the MVcannot be outside the picture boundary of the reference picture. In anexample, each reference sample in the reference block is within thereference picture.

In an embodiment, the current block is bi-predicted (e.g., encoded orreconstructed in the bi-prediction mode) with the non-merge mode (e.g.,the AMVP mode). The MV, the MVP, the MVD, the reference picture, and thereference block described above are referred to as the first MV, thefirst MVP, the first MVD, the first reference picture, and the firstreference block, respectively. A second MV of the current block can bedetermined from a second MVP and a second MVD at a second AMVRresolution. In an example, the first MVP and the second MVP aredetermined based on an MVP candidate in the MVP candidate list. Themotion information constraint can be applied for the bi-prediction inthe non-merge mode. The motion information constraint for the non-mergemode can further indicate that the second MV cannot point out of apicture boundary of a second reference picture, for example, a secondreference block pointed to by the second MV cannot be outside thepicture boundary of the second reference picture. In an example, eachsecond reference sample in the second reference block is within thesecond reference picture.

The motion information constraint described above in the non-merge modecan apply to the current block that is uni-predicted or bi-predictedusing a merge mode where, for example, the first MV and/or the second MVare determined from respective MVP(s) without an MVD.

In an embodiment, the current block is coded with an affine mode (e.g.,the affine AMVP mode or affine merge mode) and includes pluralsubblocks. In an example, each subblock in the plural subblocks hasrespective MV information (e.g., a first MV in the uni-prediction modeor an MV pair in the bi-prediction mode), such as described in FIG. 16 .

In an example, the current block is coded in the uni-prediction mode.The MV information of each subblock indicates a first MV of the subblockthat points from the subblock to a first reference subblock in a firstreference block associated with a first reference picture. The motioninformation constraint can indicate that the first MV of each subblockin the current block coded in the affine mode cannot point out of apicture boundary of the first reference picture. For example, the motioninformation constraint indicates that each first reference subblock inthe first reference block is within the first reference picture.

The above description can be adapted when the current block is coded inthe bi-prediction mode. For example, in addition to the first MV of thesubblock, the MV information of each subblock further indicates a secondMV that points from the subblock to a second reference subblock in asecond reference block associated with a second reference picture. Themotion information constraint can indicate that the first MV of eachsubblock in the current block coded in the affine mode cannot point outof the picture boundary of the first reference picture and the second MVof each subblock in the current block cannot point out of a pictureboundary of the second reference picture. For example, the motioninformation constraint further indicates that each second referencesubblock in the second reference block is within the second referencepicture.

The motion information constraint in the affine mode described above canbe applied when a subblock in the current block further includes one ormore regions where each region has a respective MV or an MV pair, forexample, the respective MV or the respective MV pair of each region isconstrained such that the respective MV or the respective MV pair ofeach region cannot point out of a respective picture boundary of arespective reference picture.

In an embodiment, if an MV points out of a picture boundary (e.g., aframe boundary), a clip operation or a clipping operation is used toensure a reference block or a portion of the reference block that ispointed to by the MV is inside (e.g., completely inside) the pictureboundary of a reference picture.

In an example, the current block is bi-predicted using the first MV andthe second MV. The first MV can point from the current block to thefirst reference block associated with the first reference picture andthe second MV can point from the current block to the second referenceblock associated with the second reference picture. If the first MVpoints out of the picture boundary of the first reference picture (e.g.,a portion of the first reference block is outside the first referencepicture), the clip operation can be used to determine a first clippedMV. The first clipped MV can point from the current block to an updatedfirst reference block where the updated first reference block is withinthe first reference picture. The clipping operation can be applied tothe second MV if a portion of the second reference block is outside thesecond reference picture, as described above.

The clipping operation described above for the bi-predicted currentblock can be adapted when the current block is uni-predicted using thefirst MV, and the first MV can be clipped as described above.

The clip operation described above can be applied if the current blockis coded with the AMVP mode where the first MV (or the second MV) isdetermined based on an MVP and an MVD. The clip operation describedabove can be applied if the current block is coded with the merge modewhere the first MV (or the second MV) is determined based on an MVPwithout an MVD. For example, the MVP is determined with an MVP indexthat points to an MVP candidate in a candidate list of the currentblock.

The clip operation described above can be applied if the current blockis coded with the affine mode, such as the affine AMVP mode, the affinemerge mode, or the like. For example, the current block is bi-predictedwith the affine mode and includes plural subblocks. In an example, asubblock in the plural subblocks includes one or more regions where eachregion in the one or more regions has respective MV information, such asan MV pair of each region. Accordingly, the subblock can be coded withone or more MV pairs associated with the respective one or more regions.In an example, the one or more regions is one region, and the subblockis the one region, for example, an MV pair of the subblock is applicableto the entire subblock, such as described in FIG. 16 .

For each region in the subblock in the plural subblocks, an MV pair caninclude (i) a respective first MV pointing from the region to a firstreference region in a first reference subblock that is in a firstreference block associated with a first reference picture and (ii) arespective second MV pointing from the region to a second referenceregion in a second reference subblock that is in a second referenceblock associated with a second reference picture. The first referenceblock and the second reference block correspond to the current block,and the first reference subblock and the second reference subblockcorrespond to the subblock. If the first reference region is outside thefirst reference picture, the clipping operation can be applied to thefirst MV. For example, a first clipped MV is determined by clipping thefirst MV such that the first clipped MV points from the region in thesubblock to an updated first reference region that is within the firstreference picture. The clipping operation can be applied to the secondMV if the second reference region is outside the second referencepicture.

The clipping operation described above for the bi-predicted currentblock with the affine mode can be adapted when the current block isuni-predicted with the affine mode. For example, each region in thesubblock of the current block is predicted based on the first referenceregion in the first reference subblock that is in the first referenceblock. The first reference region is pointed to by the first MV. Nosecond MV is used when the current block is uni-predicted. The clippingoperation is applied when the first region is outside the firstreference picture, such as described above.

An MVP candidate list of the current block can include one or more MVPcandidates. The one or more MVP candidates can include MVP candidate(s)for the uni-prediction mode and/or MVP candidate(s) for thebi-prediction mode.

According to an embodiment of the disclosure, construction of the MVPcandidate list can be constrained, for example, the MVP candidate listcan be constrained. In an example, the construction of the MVP candidatelist is constrained when the current block is coded with a merge mode.In an example, the construction of the MVP candidate list is constrainedwhen the current block is coded with a non-merge mode, such as the AMVPmode. The construction of the MVP candidate list can be constrained forthe bi-prediction mode or the uni-prediction mode.

In an example, the MVP candidate list is constrained such that one ormore of the MVP candidate(s) for the bi-prediction mode are constrained.An MVP candidate for the bi-prediction mode can include a first MVP anda second MVP. The first MVP can point from the current block to a firstintermediate reference block associated with a first reference picture.The second MVP can point from the current block to a second intermediatereference block associated with a second reference picture. The MVPcandidate for the bi-prediction mode is constrained such that the firstintermediate reference block is within the first reference picture andthe second intermediate reference block is within the second referencepicture. In an example, each of the MVP candidate(s) for thebi-prediction mode in the MVP candidate list is constrained.

In an example, the MVP candidate list is constrained such that one ormore of the MVP candidate(s) for the uni-prediction mode areconstrained. An MVP candidate for the uni-prediction mode can includeone MVP, such as the first MVP without the second MVP. The MVP candidatefor the uni-prediction mode is constrained such that the firstintermediate reference block is within the first reference picture. Inan example, each of the MVP candidate(s) for the uni-prediction mode inthe MVP candidate list is constrained.

In an example, the MVP candidate list is constrained such that (i) oneor more of the MVP candidate(s) for the bi-prediction mode areconstrained, such as described above and (ii) one or more of the MVPcandidate(s) for the uni-prediction mode are constrained, such asdescribed above.

In an embodiment, the construction of the MVP candidate list may or maynot be constrained. According to an embodiment of the disclosure, ausage of MVP candidate(s) in the MVP candidate list is constrained. TheMVP candidate list can include the MVP candidate(s) for thebi-prediction mode and the MVP candidate(s) for the uni-prediction mode.An index (e.g., an MVP index) indicating an MVP candidate (e.g., (i) afirst MVP in the uni-prediction mode or (ii) the first MVP and a secondMVP in the bi-prediction mode) in the MVP candidate list points to theMVP candidate. In the merge mode, an MV (e.g., in the uni-predictionmode) or an MV pair (e.g., in the bi-prediction mode) is determinedbased on the MVP candidate. For example, the MV is the first MVP in theuni-prediction mode. In an example, such as in the bi-prediction mode,the MV pair includes a first MV that is the first MVP and a second MVthat is the second MVP. If the MV, the first MV, or the second MV pointsout of a picture boundary (e.g., a frame boundary) of a respectivereference picture, the index cannot be selected. In an example, theindex is not selected and thus is not signaled. In an example, the MVPcandidate corresponding to the index is constrained such that the MVPcandidate cannot be used to code the current block.

A usage of affine candidate(s) in a candidate list (e.g., an affinecandidate list) can be constrained when the current block is coded inthe affine mode. As described above, the current block can include theplural subblocks. In an example, each subblock in the plural subblocksincludes one or more regions where each region in the one or moreregions has a respective MV or a respective MV pair. Motion informationof each subblock can include (i) one or more MVs (in the uni-predictionmode) or (ii) one or more MV pairs (in the bi-prediction mode) that areassociated with the respective one or more regions.

In an embodiment, the MV information of each subblock can be determinedbased on an affine candidate (e.g., an affine merge candidate) in theaffine candidate list of the current block. According to an embodimentof the disclosure, the MV information of each subblock in the currentblock can be constrained, for example, the one or more MVs (in theuni-prediction mode) or (ii) the one or more MV pairs (in thebi-prediction mode) are constrained such that (i) the one or more MVs or(ii) the one or more MV pairs cannot point out of picture boundaries ofrespective reference pictures. Otherwise, if (i) one of the one or moreMVs or (ii) an MV in the one or more MV pairs points out of a pictureboundary of a respective reference picture, the affine candidate (e.g.,an affine merge candidate) of the current block cannot be selected, forexample, to code the current block.

In an embodiment, an affine candidate list (e.g., an affine mergecandidate list) is constrained when the current block is coded in theaffine mode. The affine candidate list can include affine candidate(s).The affine candidate list can be constrained such that each of theaffine candidate(s) is constrained. In an example, an affine candidateis constrained such that MV information (e.g., (i) one or more MVs ofone or more respective regions in the subblock or (ii) one or more MVpairs of the one or more respective regions in the subblock) of eachsubblock in the current block that is determined based on the affinecandidate is within a respective picture boundary in a respectivereference picture, as described above.

Embodiments described in the application can be combined in any suitablecombination or any suitable order. For example, when the current blockis coded with the non-merge mode (e.g., the AMVP mode), each MVassociated with a respective reference picture is determined based on anMVP and an MVD. The motion information constraint of the current blockcan indicate that (i) each MV is constrained as described above (e.g., areference block pointed to by the MV is within a respective referencepicture) and (ii) the corresponding MVP is constrained (e.g., anintermediate reference block pointed to by the MVP is within therespective reference picture) as described above.

FIG. 20 shows a flow chart outlining an encoding process (2000)according to an embodiment of the disclosure. In various embodiments,the process (2000) is executed by processing circuitry, such as theprocessing circuitry in the terminal devices (310), (320), (330) and(340), processing circuitry that performs functions of a video encoder(e.g., (403), (603), (703)), or the like. In some embodiments, theprocess (2000) is implemented in software instructions, thus when theprocessing circuitry executes the software instructions, the processingcircuitry performs the process (2000). The process starts at (S2001),and proceeds to (S2010).

At (S2010), motion information of a current block to be encoded withinter prediction can be determined. The motion information can indicateone or more reference blocks of the current block associated withrespective one or more reference pictures.

At (S2020), if the one or more reference blocks are within pictureboundaries of the respective one or more reference pictures, the currentblock can be encoded based on the one or more reference blocks.

At (S2030), if a first reference region of a first reference block inthe one or more reference blocks is outside a picture boundary of afirst reference picture in the one or more reference pictures, a firstclipped MV can be determined by clipping a first motion vector (MV) suchthat an updated first reference region in an updated first referenceblock is within the picture boundary of the first reference picture. Thefirst MV indicated by the motion information can point from a region inthe current block to the first reference region, and the first clippedMV can point from the region in the current block to the updated firstreference region. The region in the current block can be encoded basedon the updated first reference region.

The process (2000) then proceeds to (S2099), and terminates.

The process (2000) can be suitably adapted to various scenarios andsteps in the process (2000) can be adjusted accordingly. One or more ofthe steps in the process (2000) can be adapted, omitted, repeated,and/or combined. Any suitable order can be used to implement the process(2000). Additional step(s) can be added.

In an example, at (S2020), if a reference block in the one or morereference blocks is outside a picture boundary of the respectivereference picture in the one or more reference pictures, updated motioninformation can be determined for the current block such that an updatedreference block indicated by the updated motion information is withinthe picture boundary of the respective reference picture in the one ormore reference pictures. The updated motion information may be signaledfor the current block and the current block can be encoded based on theupdated reference block. In this example, the step (S2030) is omitted.

FIG. 21 shows a flow chart outlining a decoding process (2100) accordingto an embodiment of the disclosure. In various embodiments, the process(2100) is executed by processing circuitry, such as the processingcircuitry in the terminal devices (310), (320), (330) and (340), theprocessing circuitry that performs functions of the video encoder (403),the processing circuitry that performs functions of the video decoder(410), the processing circuitry that performs functions of the videodecoder (510), the processing circuitry that performs functions of thevideo encoder (603), and the like. In some embodiments, the process(2100) is implemented in software instructions, thus when the processingcircuitry executes the software instructions, the processing circuitryperforms the process (2100). The process starts at (S2101), and proceedsto (S2110).

At (S2110), motion information of a current block predicted with interprediction can be determined. The motion information indicates one ormore reference blocks of the current block associated with respectiveone or more reference pictures.

At (S2120), if a motion information constraint indicates that the one ormore reference blocks are within picture boundaries of the respectiveone or more reference pictures, the current block can be reconstructedbased on the one or more reference blocks.

In an embodiment, the current block is bi-predicted with an adaptivemotion vector prediction (AMVP) mode. The motion information indicatesthe first MV pointing from the current block to the first referenceblock and a second MV pointing from the current block to a secondreference block associated with a second reference picture. The one ormore reference blocks consist of the first reference block and thesecond reference block. The motion information constraint indicates thatthe first reference block is within the picture boundary of the firstreference picture and the second reference block is within a pictureboundary of the second reference picture, the picture boundariesincluding the picture boundary of the second reference picture.

In an embodiment, the motion information indicates an MV predictor (MVP)candidate in a candidate list. The MVP candidate indicates a first MVPand a second MVP. The first MVP points to a first intermediate referenceblock that corresponds to the current block and that is within thepicture boundary of the first reference picture. The second MVP pointsto a second intermediate reference block that corresponds to the currentblock and that is within the picture boundary of the second referencepicture. The first MV is determined based on the first MVP and a firstMV difference (MVD), and a second MV is determined based on the secondMVP and a second MVD where the second MV points to the second referenceblock.

In an embodiment, the current block is bi-predicted with an affine modeand includes plural subblocks. The motion information indicates MV pairseach associated with one of the plural subblocks. Each MV pairassociated with the respective subblock in the plural subblocks includesa first MV pointing from the respective subblock to a first referencesubblock in the first reference block and a second MV pointing from therespective subblock to a second reference subblock in a second referenceblock associated with a second reference picture. The one or morereference blocks consist of first reference block and the secondreference block. The motion information constraint indicates that eachof the first reference subblocks is within the picture boundary of thefirst reference picture and each of the second reference subblocks iswithin a picture boundary of the second reference picture. The pictureboundaries include the picture boundary of the second reference picture.

In an embodiment, the current block is bi-predicted with a merge mode. Acandidate list of the current block includes one or more MV predictor(MVP) candidates. An MVP candidate of the current block can bedetermined from the one or more MVP candidates based on an MVP index.The MVP candidate indicates a first MVP associated with the firstreference picture and a second MVP associated with a second referencepicture. The first MV of the current block is determined to be the firstMVP and a second MV of the current block is determined to be the secondMVP. The motion information constraint indicates that (i) the firstreference block pointed to by the first MV is within the pictureboundary of the first reference picture, and a second reference blockpointed to by the second MV is within a picture boundary of the secondreference picture. The picture boundaries include the picture boundaryof the second reference picture.

In an example, for each MVP candidate in the one or more MVP candidatesthat indicates a respective first MVP and a respective second MVP, themotion information constraint indicates that (i) a first intermediatereference block pointed to by the respective first MVP is within apicture boundary of a respective first reference picture, and (ii) asecond intermediate reference block pointed to by the respective secondMVP is within a picture boundary of a respective second referencepicture.

In an embodiment, the current block is bi-predicted with an affine mergemode and includes plural subblocks. A candidate list of the currentblock includes one or more affine merge candidates. For each subblock inthe plural subblocks, an MV pair of the respective region can bedetermined, for each region in the respective subblock, based on anaffine merge candidate in the one or more affine merge candidates. TheMV pair includes a respective first MV pointing from the region to afirst region in a first reference subblock in the first reference blockand a respective second MV pointing from the region to a second regionin a second reference subblock that is in a second reference blockassociated with a second reference picture. The first reference blockand the second reference block correspond to the current block, and thefirst reference subblock and the second reference subblock correspond tothe respective subblock. The motion information constraint indicatesthat each first region is within the picture boundary of the firstreference picture and each second region is within a picture boundary ofthe second reference picture. The picture boundaries including thepicture boundary of the second reference picture.

At (S2130), a first motion vector (MV) indicated by the motioninformation points from a region in the current block to a firstreference region, and the first reference region is a region of a firstreference block in the one or more reference blocks. If the firstreference region is outside a picture boundary of a first referencepicture of the one or more reference pictures, a first clipped MVpointing from the region in the current block to an updated firstreference region can be determined by clipping the first MV such thatthe updated first reference region is in an updated first referenceblock that is within the picture boundary of the first referencepicture. The picture boundaries include the picture boundary of thefirst reference picture. The region in the current block can bereconstructed based on the updated first reference region.

In an embodiment, the current block is bi-predicted. The motioninformation indicates the first MV pointing from the current block tothe first reference block and a second MV pointing from the currentblock to a second reference block associated with a second referencepicture. The one or more reference blocks consist of the first referenceblock and the second reference block. The first reference region of thefirst reference block is outside the picture boundary of the firstreference picture. The first clipped MV is determined by clipping thefirst MV such that the updated first reference block is within thepicture boundary of the first reference picture. If the second referenceblock is outside a picture boundary of the second reference picture, asecond clipped MV is determined by clipping the second MV such that anupdated second reference block is within the picture boundary of thesecond reference picture. The second clipped MV points from the currentblock to the updated second reference block. The picture boundariesinclude the picture boundary of the second reference picture.

In an embodiment, the current block is bi-predicted with an affine modeand includes plural subblocks. For each subblock in the pluralsubblocks, an MV pair of the respective region is determined, for eachregion in the respective subblock, using the affine mode. The MV pairincludes a respective first MV pointing from the region to a firstreference region in a first reference subblock in the first referenceblock and a second MV pointing from the region to a second referenceregion in a second reference subblock that is in a second referenceblock associated with a second reference picture. The first referenceblock and the second reference block correspond to the current block,and the first reference subblock and the second reference subblockcorrespond to the respective subblock. The first reference region is ina first reference subblock in the first reference block, and the regionin the current block is in a subblock of the plural subblockscorresponding to the first reference subblock. The first referenceregion is outside the picture boundary of the first reference picture.The first clipped MV is determined by clipping the first MV where thefirst clipped MV points from the region in the subblock to the updatedfirst reference region.

The process (2100) proceeds to (S2199), and terminates.

The process (2100) can be suitably adapted to various scenarios andsteps in the process (2100) can be adjusted accordingly. One or more ofthe steps in the process (2100) can be adapted, omitted, repeated,and/or combined. Any suitable order can be used to implement the process(2100). Additional step(s) can be added.

Embodiments in the disclosure may be used separately or combined in anyorder. Further, each of the methods (or embodiments), an encoder, and adecoder may be implemented by processing circuitry (e.g., one or moreprocessors or one or more integrated circuits). In one example, the oneor more processors execute a program that is stored in a non-transitorycomputer-readable medium.

The techniques described above can be implemented as computer softwareusing computer-readable instructions and physically stored in one ormore computer-readable media. For example, FIG. 22 shows a computersystem (2200) suitable for implementing certain embodiments of thedisclosed subject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by one or more computer central processingunits (CPUs), Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 22 for computer system (2200) are exemplaryin nature and are not intended to suggest any limitation as to the scopeof use or functionality of the computer software implementingembodiments of the present disclosure. Neither should the configurationof components be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system (2200).

Computer system (2200) may include certain human interface inputdevices. Such a human interface input device may be responsive to inputby one or more human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard (2201), mouse (2202), trackpad (2203),touch-screen (2210), data-glove (not shown), joystick (2205), microphone(2206), scanner (2207), camera (2208).

Computer system (2200) may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen (2210), data-glove (not shown), or joystick (2205), butthere can also be tactile feedback devices that do not serve as inputdevices), audio output devices (such as: speakers (2209), headphones(not depicted)), visual output devices (such as screens (2210) toinclude CRT screens, LCD screens, plasma screens, OLED screens, eachwith or without touch-screen input capability, each with or withouttactile feedback capability—some of which may be capable to output twodimensional visual output or more than three dimensional output throughmeans such as stereographic output; virtual-reality glasses (notdepicted), holographic displays and smoke tanks (not depicted)), andprinters (not depicted).

Computer system (2200) can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW(2220) with CD/DVD or the like media (2221), thumb-drive (2222),removable hard drive or solid state drive (2223), legacy magnetic mediasuch as tape and floppy disc (not depicted), specialized ROM/ASIC/PLDbased devices such as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system (2200) can also include an interface (2254) to one ormore communication networks (2255). Networks can for example bewireless, wireline, optical. Networks can further be local, wide-area,metropolitan, vehicular and industrial, real-time, delay-tolerant, andso on. Examples of networks include local area networks such asEthernet, wireless LANs, cellular networks to include GSM, 3G, 4G, 5G,LTE and the like, TV wireline or wireless wide area digital networks toinclude cable TV, satellite TV, and terrestrial broadcast TV, vehicularand industrial to include CANBus, and so forth. Certain networkscommonly require external network interface adapters that attached tocertain general purpose data ports or peripheral buses (2249) (such as,for example USB ports of the computer system (2200)); others arecommonly integrated into the core of the computer system (2200) byattachment to a system bus as described below (for example Ethernetinterface into a PC computer system or cellular network interface into asmartphone computer system). Using any of these networks, computersystem (2200) can communicate with other entities. Such communicationcan be uni-directional, receive only (for example, broadcast TV),uni-directional send-only (for example CANbus to certain CANbusdevices), or bi-directional, for example to other computer systems usinglocal or wide area digital networks. Certain protocols and protocolstacks can be used on each of those networks and network interfaces asdescribed above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core (2240) of thecomputer system (2200).

The core (2240) can include one or more Central Processing Units (CPU)(2241), Graphics Processing Units (GPU) (2242), specialized programmableprocessing units in the form of Field Programmable Gate Areas (FPGA)(2243), hardware accelerators for certain tasks (2244), graphicsadapters (2250), and so forth. These devices, along with Read-onlymemory (ROM) (2245), Random-access memory (2246), internal mass storagesuch as internal non-user accessible hard drives, SSDs, and the like(2247), may be connected through a system bus (2248). In some computersystems, the system bus (2248) can be accessible in the form of one ormore physical plugs to enable extensions by additional CPUs, GPU, andthe like. The peripheral devices can be attached either directly to thecore's system bus (2248), or through a peripheral bus (2249). In anexample, the screen (2210) can be connected to the graphics adapter(2250). Architectures for a peripheral bus include PCI, USB, and thelike.

CPUs (2241), GPUs (2242), FPGAs (2243), and accelerators (2244) canexecute certain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM(2245) or RAM (2246). Transitional data can be stored in RAM (2246),whereas permanent data can be stored for example, in the internal massstorage (2247). Fast storage and retrieve to any of the memory devicescan be enabled through the use of cache memory, that can be closelyassociated with one or more CPU (2241), GPU (2242), mass storage (2247),ROM (2245), RAM (2246), and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture (2200), and specifically the core (2240) can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core (2240) that are of non-transitorynature, such as core-internal mass storage (2247) or ROM (2245). Thesoftware implementing various embodiments of the present disclosure canbe stored in such devices and executed by core (2240). Acomputer-readable medium can include one or more memory devices orchips, according to particular needs. The software can cause the core(2240) and specifically the processors therein (including CPU, GPU,FPGA, and the like) to execute particular processes or particular partsof particular processes described herein, including defining datastructures stored in RAM (2246) and modifying such data structuresaccording to the processes defined by the software. In addition or as analternative, the computer system can provide functionality as a resultof logic hardwired or otherwise embodied in a circuit (for example:accelerator (2244)), which can operate in place of or together withsoftware to execute particular processes or particular parts ofparticular processes described herein. Reference to software canencompass logic, and vice versa, where appropriate. Reference to acomputer-readable media can encompass a circuit (such as an integratedcircuit (IC)) storing software for execution, a circuit embodying logicfor execution, or both, where appropriate. The present disclosureencompasses any suitable combination of hardware and software.

APPENDIX A: ACRONYMS

JEM: joint exploration modelVVC: versatile video codingBMS: benchmark set

MV: Motion Vector HEVC: High Efficiency Video Coding SEI: SupplementaryEnhancement Information VUI: Video Usability Information GOPs: Groups ofPictures TUs: Transform Units, PUs: Prediction Units CTUs: Coding TreeUnits CTBs: Coding Tree Blocks PBs: Prediction Blocks HRD: HypotheticalReference Decoder SNR: Signal Noise Ratio CPUs: Central Processing UnitsGPUs: Graphics Processing Units CRT: Cathode Ray Tube LCD:Liquid-Crystal Display OLED: Organic Light-Emitting Diode CD: CompactDisc DVD: Digital Video Disc ROM: Read-Only Memory RAM: Random AccessMemory ASIC: Application-Specific Integrated Circuit PLD: ProgrammableLogic Device LAN: Local Area Network

GSM: Global System for Mobile communications

LTE: Long-Term Evolution CANBus: Controller Area Network Bus USB:Universal Serial Bus PCI: Peripheral Component Interconnect FPGA: FieldProgrammable Gate Areas

SSD: solid-state drive

IC: Integrated Circuit CU: Coding Unit R-D: Rate-Distortion

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof.

What is claimed is:
 1. A method for video decoding in a video decoder,comprising: determining motion information of a current block predictedwith inter prediction, the motion information indicating one or morereference blocks of the current block associated with respective one ormore reference pictures; in response to a motion information constraintindicating that the one or more reference blocks are within pictureboundaries of the respective one or more reference pictures,reconstructing the current block based on the one or more referenceblocks; and in response to a first motion vector (MV) indicated by themotion information pointing from a region in the current block to afirst reference region, the first reference region being a region of afirst reference block in the one or more reference blocks and beingoutside a picture boundary of a first reference picture of the one ormore reference pictures, the picture boundaries including the pictureboundary of the first reference picture; determining a first clipped MVpointing from the region in the current block to an updated firstreference region by clipping the first MV such that the updated firstreference region is in an updated first reference block that is withinthe picture boundary of the first reference picture; and reconstructingthe region in the current block based on the updated first referenceregion.
 2. The method of claim 1, wherein the current block isbi-predicted with an adaptive motion vector prediction (AMVP) mode; themotion information indicates the first MV pointing from the currentblock to the first reference block and a second MV pointing from thecurrent block to a second reference block associated with a secondreference picture; the one or more reference blocks consist of the firstreference block and the second reference block; and the motioninformation constraint indicates that the first reference block iswithin the picture boundary of the first reference picture and thesecond reference block is within a picture boundary of the secondreference picture, the picture boundaries including the picture boundaryof the second reference picture.
 3. The method of claim 2, wherein themotion information indicates an MV predictor (MVP) candidate in acandidate list, the MVP candidate indicating a first MVP and a secondMVP; the first MVP points to a first intermediate reference block thatcorresponds to the current block and that is within the picture boundaryof the first reference picture; the second MVP points to a secondintermediate reference block that corresponds to the current block andthat is within the picture boundary of the second reference picture; andthe determining the motion information includes: determining the firstMV based on the first MVP and a first MV difference (MVD); anddetermining a second MV based on the second MVP and a second MVD, thesecond MV pointing to the second reference block.
 4. The method of claim1, wherein the current block is bi-predicted with an affine mode andincludes plural subblocks; the motion information indicates MV pairseach associated with one of the plural subblocks; each MV pairassociated with the respective subblock in the plural subblocks includesa first MV pointing from the respective subblock to a first referencesubblock in the first reference block and a second MV pointing from therespective subblock to a second reference subblock in a second referenceblock associated with a second reference picture; the one or morereference blocks consist of the first reference block and the secondreference block; and the motion information constraint indicates thateach of the first reference subblocks is within the picture boundary ofthe first reference picture and each of the second reference subblocksis within a picture boundary of the second reference picture, thepicture boundaries including the picture boundary of the secondreference picture.
 5. The method of claim 1, wherein the current blockis bi-predicted with a merge mode; a candidate list of the current blockincludes one or more MV predictor (MVP) candidates; the determining themotion information includes: determining an MVP candidate of the currentblock from the one or more MVP candidates based on an MVP index, the MVPcandidate indicating a first MVP associated with the first referencepicture and a second MVP associated with a second reference picture; anddetermining the first MV of the current block to be the first MVP and asecond MV of the current block to be the second MVP; and the motioninformation constraint indicates that: the first reference block pointedto by the first MV is within the picture boundary of the first referencepicture; and a second reference block pointed to by the second MV iswithin a picture boundary of the second reference picture, the pictureboundaries including the picture boundary of the second referencepicture.
 6. The method of claim 5, wherein for each MVP candidate in theone or more MVP candidates that indicates a respective first MVP and arespective second MVP, the motion information constraint indicates that:a first intermediate reference block pointed to by the respective firstMVP is within a picture boundary of a respective first referencepicture; and a second intermediate reference block pointed to by therespective second MVP is within a picture boundary of a respectivesecond reference picture.
 7. The method of claim 1, wherein the currentblock is bi-predicted with an affine merge mode and includes pluralsubblocks; a candidate list of the current block includes one or moreaffine merge candidates; and for each subblock in the plural subblocks,the determining the motion information includes determining, for eachregion in the respective subblock, an MV pair of the respective regionbased on an affine merge candidate in the one or more affine mergecandidates, the MV pair including a respective first MV pointing fromthe region to a first region in a first reference subblock in the firstreference block and a respective second MV pointing from the region to asecond region in a second reference subblock that is in a secondreference block associated with a second reference picture, the firstreference block and the second reference block corresponding to thecurrent block, the first reference subblock and the second referencesubblock corresponding to the respective subblock; and the motioninformation constraint indicates that each first region is within thepicture boundary of the first reference picture and each second regionis within a picture boundary of the second reference picture, thepicture boundaries including the picture boundary of the secondreference picture.
 8. The method of claim 1, wherein the current blockis bi-predicted; the motion information indicates the first MV pointingfrom the current block to the first reference block and a second MVpointing from the current block to a second reference block associatedwith a second reference picture; the one or more reference blocksconsist of the first reference block and the second reference block; thefirst reference region of the first reference block is outside thepicture boundary of the first reference picture; the determining thefirst clipped MV includes determining the first clipped MV by clippingthe first MV such that the updated first reference block is within thepicture boundary of the first reference picture; and in response to thesecond reference block being outside a picture boundary of the secondreference picture, determining a second clipped MV by clipping thesecond MV such that an updated second reference block is within thepicture boundary of the second reference picture, the second clipped MVpointing from the current block to the updated second reference block,the picture boundaries including the picture boundary of the secondreference picture.
 9. The method of claim 1, wherein the current blockis bi-predicted with an affine mode and includes plural subblocks; foreach subblock in the plural subblocks, the determining the motioninformation includes determining, for each region in the respectivesubblock, an MV pair of the respective region using the affine mode, theMV pair including a respective first MV pointing from the region to thefirst reference region in a first reference subblock in the firstreference block and a second MV pointing from the region to a secondreference region in a second reference subblock that is in a secondreference block associated with a second reference picture, the firstreference block and the second reference block corresponding to thecurrent block, the first reference subblock and the second referencesubblock corresponding to the respective subblock; the first referenceregion is in the first reference subblock in the first reference block,the region in the current block being in a subblock of the pluralsubblocks corresponding to the first reference subblock; the firstreference region is outside the picture boundary of the first referencepicture; and the determining the first clipped MV includes determiningthe first clipped MV by clipping the first MV, the first clipped MVpointing from the region in the subblock to the updated first referenceregion.
 10. An apparatus for video decoding, comprising: processingcircuitry configured to: determine motion information of a current blockpredicted with inter prediction, the motion information indicating oneor more reference blocks of the current block associated with respectiveone or more reference pictures; in response to a motion informationconstraint indicating that the one or more reference blocks are withinpicture boundaries of the respective one or more reference pictures,reconstruct the current block based on the one or more reference blocks;and in response to a first motion vector (MV) indicated by the motioninformation pointing from a region in the current block to a firstreference region, the first reference region being a region of a firstreference block in the one or more reference blocks and being outside apicture boundary of a first reference picture of the one or morereference pictures, the picture boundaries including the pictureboundary of the first reference picture; determine a first clipped MVpointing from the region in the current block to an updated firstreference region by clipping the first MV such that the updated firstreference region is in an updated first reference block that is withinthe picture boundary of the first reference picture; and reconstruct theregion in the current block based on the updated first reference region.11. The apparatus of claim 10, wherein the current block is bi-predictedwith an adaptive motion vector prediction (AMVP) mode; the motioninformation indicates the first MV pointing from the current block tothe first reference block and a second MV pointing from the currentblock to a second reference block associated with a second referencepicture; the one or more reference blocks consist of the first referenceblock and the second reference block; and the motion informationconstraint indicates that the first reference block is within thepicture boundary of the first reference picture and the second referenceblock is within a picture boundary of the second reference picture, thepicture boundaries including the picture boundary of the secondreference picture.
 12. The apparatus of claim 11, wherein the motioninformation indicates an MV predictor (MVP) candidate in a candidatelist, the MVP candidate indicating a first MVP and a second MVP; thefirst MVP points to a first intermediate reference block thatcorresponds to the current block and that is within the picture boundaryof the first reference picture; the second MVP points to a secondintermediate reference block that corresponds to the current block andthat is within the picture boundary of the second reference picture; andthe processing circuitry is configured to: determine the first MV basedon the first MVP and a first MV difference (MVD); and determine a secondMV based on the second MVP and a second MVD, the second MV pointing tothe second reference block.
 13. The apparatus of claim 10, wherein thecurrent block is bi-predicted with an affine mode and includes pluralsubblocks; the motion information indicates MV pairs each associatedwith one of the plural subblocks; each MV pair associated with therespective subblock in the plural subblocks includes a first MV pointingfrom the respective subblock to a first reference subblock in the firstreference block and a second MV pointing from the respective subblock toa second reference subblock in a second reference block associated witha second reference picture; the one or more reference blocks consist ofthe first reference block and the second reference block; and the motioninformation constraint indicates that each of the first referencesubblocks is within the picture boundary of the first reference pictureand each of the second reference subblocks is within a picture boundaryof the second reference picture, the picture boundaries including thepicture boundary of the second reference picture.
 14. The apparatus ofclaim 10, wherein the current block is bi-predicted with a merge mode; acandidate list of the current block includes one or more MV predictor(MVP) candidates; the processing circuitry is configured to: determinean MVP candidate of the current block from the one or more MVPcandidates based on an MVP index, the MVP candidate indicating a firstMVP associated with the first reference picture and a second MVPassociated with a second reference picture; and determine the first MVof the current block to be the first MVP and a second MV of the currentblock to be the second MVP; and the motion information constraintindicates that: the first reference block pointed to by the first MV iswithin the picture boundary of the first reference picture; and a secondreference block pointed to by the second MV is within a picture boundaryof the second reference picture, the picture boundaries including thepicture boundary of the second reference picture.
 15. The apparatus ofclaim 14, wherein for each MVP candidate in the one or more MVPcandidates that indicates a respective first MVP and a respective secondMVP, the motion information constraint indicates that: a firstintermediate reference block pointed to by the respective first MVP iswithin a picture boundary of a respective first reference picture; and asecond intermediate reference block pointed to by the respective secondMVP is within a picture boundary of a respective second referencepicture.
 16. The apparatus of claim 10, wherein the current block isbi-predicted with an affine merge mode and includes plural subblocks; acandidate list of the current block includes one or more affine mergecandidates; and for each subblock in the plural subblocks, theprocessing circuitry is configured to determine, for each region in therespective subblock, an MV pair of the respective region based on anaffine merge candidate in the one or more affine merge candidates, theMV pair including a respective first MV pointing from the region to afirst region in a first reference subblock in the first reference blockand a second MV pointing from the region to a second region in a secondreference subblock that is in a second reference block associated with asecond reference picture, the first reference block and the secondreference block corresponding to the current block, the first referencesubblock and the second reference subblock corresponding to therespective subblock; and the motion information constraint indicatesthat each first region is within the picture boundary of the firstreference picture and each second region is within a picture boundary ofthe second reference picture, the picture boundaries including thepicture boundary of the second reference picture.
 17. The apparatus ofclaim 10, wherein the current block is bi-predicted; the motioninformation indicates the first MV pointing from the current block tothe first reference block and a second MV pointing from the currentblock to a second reference block associated with a second referencepicture; the one or more reference blocks consist of the first referenceblock and the second reference block; the first reference region of thefirst reference block is outside the picture boundary of the firstreference picture; and the processing circuitry is configured to:determine the first clipped MV by clipping the first MV such that theupdated first reference block is within the picture boundary of thefirst reference picture; and in response to the second reference blockbeing outside a picture boundary of the second reference picture,determine a second clipped MV by clipping the second MV such that anupdated second reference block is within the picture boundary of thesecond reference picture, the second clipped MV pointing from thecurrent block to the updated second reference block, the pictureboundaries including the picture boundary of the second referencepicture.
 18. The apparatus of claim 10, wherein the current block isbi-predicted with an affine mode and includes plural subblocks; for eachsubblock in the plural subblocks, the processing circuitry is configuredto determine, for each region in the respective subblock, an MV pair ofthe respective region using the affine mode, the MV pair including arespective first MV pointing from the region to the first referenceregion in a first reference subblock in the first reference block and asecond MV pointing from the region to a second reference region in asecond reference subblock that is in a second reference block associatedwith a second reference picture, the first reference block and thesecond reference block corresponding to the current block, the firstreference subblock and the second reference subblock corresponding tothe respective subblock; the first reference region is in the firstreference subblock in the first reference block, the region in thecurrent block being in a subblock of the plural subblocks correspondingto the first reference subblock; the first reference region is outsidethe picture boundary of the first reference picture; and the processingcircuitry is configured to determine the first clipped MV by clippingthe first MV, the first clipped MV pointing from the region in thesubblock to the updated first reference region.
 19. A non-transitorycomputer-readable storage medium storing a program executable by atleast one processor to perform: determining motion information of acurrent block predicted with inter prediction, the motion informationindicating one or more reference blocks of the current block associatedwith respective one or more reference pictures; in response to a motioninformation constraint indicating that the one or more reference blocksare within picture boundaries of the respective one or more referencepictures, reconstructing the current block based on the one or morereference blocks; and in response to a first motion vector (MV)indicated by the motion information pointing from a region in thecurrent block to a first reference region, the first reference regionbeing a region of a first reference block in the one or more referenceblocks and being outside a picture boundary of a first reference pictureof the one or more reference pictures, the picture boundaries includingthe picture boundary of the first reference picture; determining a firstclipped MV pointing from the region in the current block to an updatedfirst reference region by clipping the first MV such that the updatedfirst reference region is in an updated first reference block that iswithin the picture boundary of the first reference picture; andreconstructing the region in the current block based on the updatedfirst reference region.
 20. The non-transitory computer-readable storagemedium of claim 19, wherein the current block is bi-predicted with anadaptive motion vector prediction (AMVP) mode; the motion informationindicates the first MV pointing from the current block to the firstreference block and a second MV pointing from the current block to asecond reference block associated with a second reference picture; theone or more reference blocks consist of the first reference block andthe second reference block; and the motion information constraintindicates that the first reference block is within the picture boundaryof the first reference picture and the second reference block is withina picture boundary of the second reference picture, the pictureboundaries including the picture boundary of the second referencepicture.